BACKGROUND Extragonadal yolk sac tumors(YSTs)are rare,with only a low reported tumor occurrence outside the gonads locally and abroad.Extragonadal YSTs are usually a diagnostic challenge,because they are infrequent,bu...BACKGROUND Extragonadal yolk sac tumors(YSTs)are rare,with only a low reported tumor occurrence outside the gonads locally and abroad.Extragonadal YSTs are usually a diagnostic challenge,because they are infrequent,but also because a thoughtful and detailed differential diagnostic process must be performed.CASE SUMMARY Here we present a case of an abdominal wall YST in a 20-year-old woman admitted with a tumor in the lower abdomen close to the umbilicus.The tumorectomy was performed.The histological examination revealed characteristic findings such as Schiller-Duval bodies,loose reticular structures,papillary structures,and eosinophilic globules.According to the immunohistochemical staining,the tumor tissue was positive for broad-spectrum cytokeratin,Spalt-like transcription factor 4,glypican-3,CD117,and epithelial membrane antigen.Based on the clinical information,histological features,and immunohistochemical staining profile,the tumor was diagnosed as a YST present in the abdominal wall.CONCLUSION Based on the clinical information,histological features,and immunohistochemical staining profile described above,the tumor was diagnosed as a primary YST in the abdominal wall.展开更多
Yolk sac tumors of the ovary are rare entities that account for 2% - 5% of all ovarian tumors. They represent the second most common histological variant of malignant germ cell tumors of the ovary after dysgerminomas....Yolk sac tumors of the ovary are rare entities that account for 2% - 5% of all ovarian tumors. They represent the second most common histological variant of malignant germ cell tumors of the ovary after dysgerminomas. Yolk sac tumors are most commonly encountered in women in the second and third decades. Microscopically, they are highly polymorphic and can present in a pure form or associated with another contingent of germ cell tumor. We report the case of a 26-year-old woman, who underwent surgery for a large right ovarian tumor rupturing into the peritoneal cavity. The ovarian tumor was revealed by ascites of great abundance and abdomino-pelvic pain. On histological examination, the diagnosis of yolk sac tumor in its pure and polyvesicular vitelline pattern was made. Through this observation, we propose to discuss the anatomoclinical particularities of these tumors by emphasizing the importance of histology for the diagnosis as well as the need of an early and appropriate management.展开更多
Yolk sac tumors (YSTs) are rare malignant germ cell tumors that usually affect youngfemales. To date, there have been few studies on YSTs. We evaluated the relationship betweenclinicopathologic characteristics of pati...Yolk sac tumors (YSTs) are rare malignant germ cell tumors that usually affect youngfemales. To date, there have been few studies on YSTs. We evaluated the relationship betweenclinicopathologic characteristics of patients with ovarian YSTs and disease outcome based onSurveillance, Epidemiology, and End Results data. The K aplan-Meier method and log-rank testwere used to evaluate differences in survival rates. Data for 269 patients were analyzed. Theincidence of YSTs among ovarian germ cell tumors (OGCTs) cases was 0.4%;median patient agewas 22.0 years, and most tumors were unilateral. Patients presented with distant metastasis (37.5%),localized disease (49. 1%), and regional spread (8.9%). American Joint Committee on Cancer stagewas available for 13 patients (stage IA, n=2;stage IC, n=1;stage IA, n=1;stage IB, n=3;stageIlC, n=2;and stage IV, n=4). Survival rates at 1, 3, and 5 years were 91.0%, 84.0%, and 83.2%,respectively, for overall survival (OS) and 92.0%, 85.4%, and 84.5%, respectively, for disease-specific survival (DSS). The 5-year OS and DSS of patients with ovary tumors were 91.5% and92.9%, respectively, compared to 74.8% and 77.2%, respectively, for those with extra-ovarianspread (P<0.001 for both OS and DSS). Age >50 years was associated with shorter OS and DSS(both P<0.001), whereas no associatios of OS and DSS were observed with pathologic grade (P=0.49for OS and 0.52 for DSS). In summary, YSTs are typically unilateral, of a high grade, and localizedto the ovary;extra-ovarian spread has a poor outcome, and postmenopausal women have worseprognosis than premenopausal women.展开更多
Yolk sac tumor (YST), which most frequently arises in the gonads as a type of germ cell tumor, is rare in children but is highly malignant. The common age grou</span><span style="font-family:Verdana;&quo...Yolk sac tumor (YST), which most frequently arises in the gonads as a type of germ cell tumor, is rare in children but is highly malignant. The common age grou</span><span style="font-family:Verdana;">p affected by yolk sac tumours is 11 to 24 years. In this study, we described a rare case of YST in terms of the clinical manifestation, imaging, and h</span><span style="font-family:Verdana;">istopathology findings, diagnosis and treatment in a 12-year-old girl who was followed since birth for Fanconi-like syndrome. This is a rare clinical association that also limits chemotherapy.展开更多
Background: Ovarian Yolk sac tumor (OYST) is a rare entity of malignant ovarian germ cell tumors (MOGCT). Abdominal pain, a rapidly growing distending mass or irregular vaginal bleeding is the main presentation. Serum...Background: Ovarian Yolk sac tumor (OYST) is a rare entity of malignant ovarian germ cell tumors (MOGCT). Abdominal pain, a rapidly growing distending mass or irregular vaginal bleeding is the main presentation. Serum AFP is elevated in nearly all cases. The standard management is fertility preserving surgery with adjuvant chemotherapy. Aim of Work: To report and analyze retrospectively recorded cases that were either treated at National Cancer Institute/Egypt or referred there for advice about therapy. Materials and Methods: This is a retrospective single-institutional analysis of 18 cases of OYST treated at National Cancer Institute-Cairo University from January 2011 till December 2015. The clinical and pathological characteristics, treatment, and outcomes of these patients were analyzed. Results: Data from eighteen patients were obtained. The median age was 18 years (range: 15 - 22). Abdominal pain was the most common presentation (89%). The mean tumor size was 21cm (range: 8 - 30 cm). Eleven of our cases (61%) were stage I, seven cases and (39%) were stage IV at presentation. Fifteen cases (83%) underwent fertility preserving procedure & the standard surgical staging. Panhysterectomy & formal staging procedure was done only in two cases (11%). One case (6%) underwent bilateral salpingo-oophorectomy. 2 cases (11.1%) only underwent lymph node biopsy. 11 patient (61.1%) showed pure type YST while mixed type was present in the remaining 7 cases (38.8%): Dysgerminoma (one case, 5.6%), Dysgerminoma + immature teratoma (one case, 5.6%), Immature teratoma (2 cases, 11.1%) and Teratoma (3 cases, 16.7%). AFP was extremely elevated in all cases at presentation (median 4191 ng/mL;ranging: 725 ng/mL - 402,908 ng/mL). It showed decreased level after surgery (median 145 ng/ mL;ranging: 2 ng/mL - 38,000 ng/mL) & normalized after chemotherapy except for progressive disease. All cases started BEP regimen after surgery with complete remission in twelve cases. In follow up period (median 17 months;ranging: 2 - 48 months) two patients relapsed;the mean overall survival time was 34.2 and progression free survival was 33.84 months respectively. Conclusion: Ovarian yolk sac tumors are rare neoplasms. Surgery with adjuvant chemotherapy is the standard management. AFP is important for diagnosis, monitoring response to treatment and predicting relapse.展开更多
Extragonadal primary yolk sac tumor of the intestinal tract origin is exceedingly rare. Through a multiple disciplinary team, the diagnosis and treatment of primary intestinal yolk sac tumor were further defined. We r...Extragonadal primary yolk sac tumor of the intestinal tract origin is exceedingly rare. Through a multiple disciplinary team, the diagnosis and treatment of primary intestinal yolk sac tumor were further defined. We report 2 such cases with detailed histologic and immunohistochemical analysis. The two patients were a 7-year-old girl and a 29-year-old woman. Both of them preoperatively had an elevated serum alpha fetoprotein(AFP) level(≥ 1,210 ng/mL). The tumors are located in the intestine and imaging examination indicated the rectum as the primary site. Grossly the mass was grey-white and crisp texture. Microscopic examination featured reticular, microcystic, macrocystic, papillary, solid, and some glandular patterns. Immunohistochemically,tumor cells of both cases were positive for SALL4, AFP, pan-cytokeratin(AE1/AE3), and glypican-3. Simultaneously, a stain for EMA, OCT4, CD30, HCG, vimentin and CK20 were negative in all 2 neoplasms. The features of morphology,immunohistochemistry, laboratory examinations and imaging studies consist of the diagnosis of primary yolk sac tumor of the intestine.展开更多
Primary yolk sac tumor of the mediastinum is very rare. Yolk sac tumor is highly malignant, and has less chance of operation. One case, which treated in this institute since 1954, is retrospectively studied to investi...Primary yolk sac tumor of the mediastinum is very rare. Yolk sac tumor is highly malignant, and has less chance of operation. One case, which treated in this institute since 1954, is retrospectively studied to investigate the clinical characteristics, surgical treatment and prognosis of the primary mediastinal yolk sac tumor.展开更多
Sacrococcygeal teratoma (SCT) is a common congenital neoplasm, contains derivatives of more than one of the three embryonic germ cell layers. However, malignant Sacrococcygeal Yolk Sac tumor (YST) is an extremely rare...Sacrococcygeal teratoma (SCT) is a common congenital neoplasm, contains derivatives of more than one of the three embryonic germ cell layers. However, malignant Sacrococcygeal Yolk Sac tumor (YST) is an extremely rare extra-gonadal germ cell tumor. This case describes a two and half years old female child presenting with history of swelling at sacrococcygeal region for nine months. Case was evaluated clinically. Patient’s serum alpha fetoprotein (AFP) level was elevated abnormally. FNAC of the swelling was done which shows suspicious cell for immature teratoma. Swelling excised and histopathological examination was carried out, the report of which shows malignant sacrococcygeal teratoma with yolk sac tumor.展开更多
BACKGROUND Conjoined twins are a rare twin malformation commonly presenting as single amniotic sac twinning,with double amniotic sac twinning being extremely rare and poorly reported.Most conjoined twins are females.C...BACKGROUND Conjoined twins are a rare twin malformation commonly presenting as single amniotic sac twinning,with double amniotic sac twinning being extremely rare and poorly reported.Most conjoined twins are females.CASE SUMMARY A woman of childbearing age conceived naturally,and at 8 wk of gestation,transvaginal ultrasonography showed an embryo and cardiac tube pulsation in both amniotic sacs.On dynamic observation,the two embryos were connected in the lower abdomen,with restricted movement.A repeat transvaginal ultrasound at 11 wk showed that the intestinal tubes of both fetuses were connected in the lower abdomen.The pregnancy was terminated and labor was induced.CONCLUSION Transvaginal ultrasound may detect conjoined twin malformations in an early stage.Our case provides diagnostic insights for ultrasonographers and can help develop early therapeutic interventions.展开更多
During embryogenesis,hematopoietic stem progenitor cells(HSPCs)are believed to be derived from hemogenic endothelial cells(HECs).Moreover,arterial feature is proposed to be a prerequisite for HECs to generate HSPCs wi...During embryogenesis,hematopoietic stem progenitor cells(HSPCs)are believed to be derived from hemogenic endothelial cells(HECs).Moreover,arterial feature is proposed to be a prerequisite for HECs to generate HSPCs with lymphoid potential.Although the molecular basis of hematopoietic stem cell-competent HECs has been delicately elucidated within the embryo proper,the functional and molecular characteristics of HECs in the extraembryonic yolk sac(YS)remain largely unresolved.In this study,we initially identified six molecularly different endothelial populations in the midgestational YS through integrated analysis of several single-cell RNA sequencing(scRNA-seq)datasets and validated the arterial vasculature distribution of Gja5+ECs using a Gja5-EGFP reporter mouse model.Further,we explored the hemogenic potential of different EC populations based on their Gja5-EGFP and CD44 expression levels.The hemogenic potential was ubiquitously detected in spatiotemporally different vascular beds on embryonic days(E)8.5–E9.5 and gradually concentrated in CD44-positive ECs from E10.0.Unexpectedly,B-lymphoid potential was detected in the YS ECs as early as E8.5 regardless of their arterial features.Furthermore,the capacity for generating hematopoietic progenitors with in vivo lymphoid potential was found in nonarterial as well as arterial YS ECs on E10.0–E10.5.Importantly,the distinct identities of E10.0–E10.5 HECs between YS and intraembryonic caudal region were revealed by further scRNA-seq analysis.Cumulatively,these findings extend our knowledge regarding the hemogenic potential of ECs from anatomically and molecularly different vascular beds,providing a theoretical basis for better understanding the sources of HSPCs during mammalian development.展开更多
Changes in quantities of water, sodium, potassium, lipid and protein were compared in developing eggs and yolk-sac larvae of herring dupes harengus L., a species with demersal eggs, and plaice Pleuroncctcs platessa L....Changes in quantities of water, sodium, potassium, lipid and protein were compared in developing eggs and yolk-sac larvae of herring dupes harengus L., a species with demersal eggs, and plaice Pleuroncctcs platessa L., a species with pelagic eggs. The principal difference between the two species was the occurrence in herring, but not in plaice of considerable increases in water content and in one or both of the above ions at three distinct stages: at fertilization,during the middle stage of egg development, and in the days immediately after hatching. Newly hatched larvae of the two species differed greatly in water content because of the difference in mass and water content of the yolk, not in the water content of the rest of the body. In herring, there were increases in sodium and potassium which coincided broadly with the increase in water content. These differences are related to the gradual acquisition of buoyancy by herring during this period, comparable with the buoyancy conferred on plaice eggs展开更多
基金Supported by National Natural Science Foundation of China(Grant No.82103624 to Wang Y)Horizontal Project of Jinzhou Medical University(Grant No.STC-2S21094 to Yang J).
文摘BACKGROUND Extragonadal yolk sac tumors(YSTs)are rare,with only a low reported tumor occurrence outside the gonads locally and abroad.Extragonadal YSTs are usually a diagnostic challenge,because they are infrequent,but also because a thoughtful and detailed differential diagnostic process must be performed.CASE SUMMARY Here we present a case of an abdominal wall YST in a 20-year-old woman admitted with a tumor in the lower abdomen close to the umbilicus.The tumorectomy was performed.The histological examination revealed characteristic findings such as Schiller-Duval bodies,loose reticular structures,papillary structures,and eosinophilic globules.According to the immunohistochemical staining,the tumor tissue was positive for broad-spectrum cytokeratin,Spalt-like transcription factor 4,glypican-3,CD117,and epithelial membrane antigen.Based on the clinical information,histological features,and immunohistochemical staining profile,the tumor was diagnosed as a YST present in the abdominal wall.CONCLUSION Based on the clinical information,histological features,and immunohistochemical staining profile described above,the tumor was diagnosed as a primary YST in the abdominal wall.
文摘Yolk sac tumors of the ovary are rare entities that account for 2% - 5% of all ovarian tumors. They represent the second most common histological variant of malignant germ cell tumors of the ovary after dysgerminomas. Yolk sac tumors are most commonly encountered in women in the second and third decades. Microscopically, they are highly polymorphic and can present in a pure form or associated with another contingent of germ cell tumor. We report the case of a 26-year-old woman, who underwent surgery for a large right ovarian tumor rupturing into the peritoneal cavity. The ovarian tumor was revealed by ascites of great abundance and abdomino-pelvic pain. On histological examination, the diagnosis of yolk sac tumor in its pure and polyvesicular vitelline pattern was made. Through this observation, we propose to discuss the anatomoclinical particularities of these tumors by emphasizing the importance of histology for the diagnosis as well as the need of an early and appropriate management.
文摘Yolk sac tumors (YSTs) are rare malignant germ cell tumors that usually affect youngfemales. To date, there have been few studies on YSTs. We evaluated the relationship betweenclinicopathologic characteristics of patients with ovarian YSTs and disease outcome based onSurveillance, Epidemiology, and End Results data. The K aplan-Meier method and log-rank testwere used to evaluate differences in survival rates. Data for 269 patients were analyzed. Theincidence of YSTs among ovarian germ cell tumors (OGCTs) cases was 0.4%;median patient agewas 22.0 years, and most tumors were unilateral. Patients presented with distant metastasis (37.5%),localized disease (49. 1%), and regional spread (8.9%). American Joint Committee on Cancer stagewas available for 13 patients (stage IA, n=2;stage IC, n=1;stage IA, n=1;stage IB, n=3;stageIlC, n=2;and stage IV, n=4). Survival rates at 1, 3, and 5 years were 91.0%, 84.0%, and 83.2%,respectively, for overall survival (OS) and 92.0%, 85.4%, and 84.5%, respectively, for disease-specific survival (DSS). The 5-year OS and DSS of patients with ovary tumors were 91.5% and92.9%, respectively, compared to 74.8% and 77.2%, respectively, for those with extra-ovarianspread (P<0.001 for both OS and DSS). Age >50 years was associated with shorter OS and DSS(both P<0.001), whereas no associatios of OS and DSS were observed with pathologic grade (P=0.49for OS and 0.52 for DSS). In summary, YSTs are typically unilateral, of a high grade, and localizedto the ovary;extra-ovarian spread has a poor outcome, and postmenopausal women have worseprognosis than premenopausal women.
文摘Yolk sac tumor (YST), which most frequently arises in the gonads as a type of germ cell tumor, is rare in children but is highly malignant. The common age grou</span><span style="font-family:Verdana;">p affected by yolk sac tumours is 11 to 24 years. In this study, we described a rare case of YST in terms of the clinical manifestation, imaging, and h</span><span style="font-family:Verdana;">istopathology findings, diagnosis and treatment in a 12-year-old girl who was followed since birth for Fanconi-like syndrome. This is a rare clinical association that also limits chemotherapy.
文摘Background: Ovarian Yolk sac tumor (OYST) is a rare entity of malignant ovarian germ cell tumors (MOGCT). Abdominal pain, a rapidly growing distending mass or irregular vaginal bleeding is the main presentation. Serum AFP is elevated in nearly all cases. The standard management is fertility preserving surgery with adjuvant chemotherapy. Aim of Work: To report and analyze retrospectively recorded cases that were either treated at National Cancer Institute/Egypt or referred there for advice about therapy. Materials and Methods: This is a retrospective single-institutional analysis of 18 cases of OYST treated at National Cancer Institute-Cairo University from January 2011 till December 2015. The clinical and pathological characteristics, treatment, and outcomes of these patients were analyzed. Results: Data from eighteen patients were obtained. The median age was 18 years (range: 15 - 22). Abdominal pain was the most common presentation (89%). The mean tumor size was 21cm (range: 8 - 30 cm). Eleven of our cases (61%) were stage I, seven cases and (39%) were stage IV at presentation. Fifteen cases (83%) underwent fertility preserving procedure & the standard surgical staging. Panhysterectomy & formal staging procedure was done only in two cases (11%). One case (6%) underwent bilateral salpingo-oophorectomy. 2 cases (11.1%) only underwent lymph node biopsy. 11 patient (61.1%) showed pure type YST while mixed type was present in the remaining 7 cases (38.8%): Dysgerminoma (one case, 5.6%), Dysgerminoma + immature teratoma (one case, 5.6%), Immature teratoma (2 cases, 11.1%) and Teratoma (3 cases, 16.7%). AFP was extremely elevated in all cases at presentation (median 4191 ng/mL;ranging: 725 ng/mL - 402,908 ng/mL). It showed decreased level after surgery (median 145 ng/ mL;ranging: 2 ng/mL - 38,000 ng/mL) & normalized after chemotherapy except for progressive disease. All cases started BEP regimen after surgery with complete remission in twelve cases. In follow up period (median 17 months;ranging: 2 - 48 months) two patients relapsed;the mean overall survival time was 34.2 and progression free survival was 33.84 months respectively. Conclusion: Ovarian yolk sac tumors are rare neoplasms. Surgery with adjuvant chemotherapy is the standard management. AFP is important for diagnosis, monitoring response to treatment and predicting relapse.
基金supported by Tianjin Municipal Health Bureau Science and Technology Foundation(Grant No.16KG125)National Clinical Research Center for Cancer
文摘Extragonadal primary yolk sac tumor of the intestinal tract origin is exceedingly rare. Through a multiple disciplinary team, the diagnosis and treatment of primary intestinal yolk sac tumor were further defined. We report 2 such cases with detailed histologic and immunohistochemical analysis. The two patients were a 7-year-old girl and a 29-year-old woman. Both of them preoperatively had an elevated serum alpha fetoprotein(AFP) level(≥ 1,210 ng/mL). The tumors are located in the intestine and imaging examination indicated the rectum as the primary site. Grossly the mass was grey-white and crisp texture. Microscopic examination featured reticular, microcystic, macrocystic, papillary, solid, and some glandular patterns. Immunohistochemically,tumor cells of both cases were positive for SALL4, AFP, pan-cytokeratin(AE1/AE3), and glypican-3. Simultaneously, a stain for EMA, OCT4, CD30, HCG, vimentin and CK20 were negative in all 2 neoplasms. The features of morphology,immunohistochemistry, laboratory examinations and imaging studies consist of the diagnosis of primary yolk sac tumor of the intestine.
文摘Primary yolk sac tumor of the mediastinum is very rare. Yolk sac tumor is highly malignant, and has less chance of operation. One case, which treated in this institute since 1954, is retrospectively studied to investigate the clinical characteristics, surgical treatment and prognosis of the primary mediastinal yolk sac tumor.
文摘Sacrococcygeal teratoma (SCT) is a common congenital neoplasm, contains derivatives of more than one of the three embryonic germ cell layers. However, malignant Sacrococcygeal Yolk Sac tumor (YST) is an extremely rare extra-gonadal germ cell tumor. This case describes a two and half years old female child presenting with history of swelling at sacrococcygeal region for nine months. Case was evaluated clinically. Patient’s serum alpha fetoprotein (AFP) level was elevated abnormally. FNAC of the swelling was done which shows suspicious cell for immature teratoma. Swelling excised and histopathological examination was carried out, the report of which shows malignant sacrococcygeal teratoma with yolk sac tumor.
文摘BACKGROUND Conjoined twins are a rare twin malformation commonly presenting as single amniotic sac twinning,with double amniotic sac twinning being extremely rare and poorly reported.Most conjoined twins are females.CASE SUMMARY A woman of childbearing age conceived naturally,and at 8 wk of gestation,transvaginal ultrasonography showed an embryo and cardiac tube pulsation in both amniotic sacs.On dynamic observation,the two embryos were connected in the lower abdomen,with restricted movement.A repeat transvaginal ultrasound at 11 wk showed that the intestinal tubes of both fetuses were connected in the lower abdomen.The pregnancy was terminated and labor was induced.CONCLUSION Transvaginal ultrasound may detect conjoined twin malformations in an early stage.Our case provides diagnostic insights for ultrasonographers and can help develop early therapeutic interventions.
基金supported by the National Key Research and Development Program of China(2020YFA0112402,2017YFA0103401,and 2016YFA0100601)the National Natural Science Foundation of China(81890991,31930054,31871173,82000111,and 81900115)+1 种基金the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(2017ZT07S347)the Key Research and Development Program of Guangdong Province(2019B020234002)。
文摘During embryogenesis,hematopoietic stem progenitor cells(HSPCs)are believed to be derived from hemogenic endothelial cells(HECs).Moreover,arterial feature is proposed to be a prerequisite for HECs to generate HSPCs with lymphoid potential.Although the molecular basis of hematopoietic stem cell-competent HECs has been delicately elucidated within the embryo proper,the functional and molecular characteristics of HECs in the extraembryonic yolk sac(YS)remain largely unresolved.In this study,we initially identified six molecularly different endothelial populations in the midgestational YS through integrated analysis of several single-cell RNA sequencing(scRNA-seq)datasets and validated the arterial vasculature distribution of Gja5+ECs using a Gja5-EGFP reporter mouse model.Further,we explored the hemogenic potential of different EC populations based on their Gja5-EGFP and CD44 expression levels.The hemogenic potential was ubiquitously detected in spatiotemporally different vascular beds on embryonic days(E)8.5–E9.5 and gradually concentrated in CD44-positive ECs from E10.0.Unexpectedly,B-lymphoid potential was detected in the YS ECs as early as E8.5 regardless of their arterial features.Furthermore,the capacity for generating hematopoietic progenitors with in vivo lymphoid potential was found in nonarterial as well as arterial YS ECs on E10.0–E10.5.Importantly,the distinct identities of E10.0–E10.5 HECs between YS and intraembryonic caudal region were revealed by further scRNA-seq analysis.Cumulatively,these findings extend our knowledge regarding the hemogenic potential of ECs from anatomically and molecularly different vascular beds,providing a theoretical basis for better understanding the sources of HSPCs during mammalian development.
文摘Changes in quantities of water, sodium, potassium, lipid and protein were compared in developing eggs and yolk-sac larvae of herring dupes harengus L., a species with demersal eggs, and plaice Pleuroncctcs platessa L., a species with pelagic eggs. The principal difference between the two species was the occurrence in herring, but not in plaice of considerable increases in water content and in one or both of the above ions at three distinct stages: at fertilization,during the middle stage of egg development, and in the days immediately after hatching. Newly hatched larvae of the two species differed greatly in water content because of the difference in mass and water content of the yolk, not in the water content of the rest of the body. In herring, there were increases in sodium and potassium which coincided broadly with the increase in water content. These differences are related to the gradual acquisition of buoyancy by herring during this period, comparable with the buoyancy conferred on plaice eggs
