背联体贻贝棘尾虫的形态、形态发生及其调节现象

THE MORPHOLOGY MORPHOGENESIS, AND THEIR REGULATION OF DORSI-CONNECTED STYLONYCHIA MYTILUS

背联体贻贝棘尾虫的每一虫腹面含有相当于正常棘尾虫的腹面纤毛系统,背联两虫任意一侧属于一虫的背面有4列背触毛,它们的排列分布相似于正常棘昆虫的第1—4列背触毛,另一虫背面打2列背触毛,它们相似于正常棘尾虫的第5、6列背触毛。结果表明,背联体棘尾虫是其中两虫各以背面第4列和第5列背触毛之间的皮层区相联接形成的。也有的背联体中背部皮层联接区有变化。无性分裂中背联两虫皮层纤毛结构的形态发生相似于正常棘尾虫,并且两者其皮层纤毛器如口围带、额腹横棘毛、左、右缘棘毛和背触毛等相应结构的发育是同步进行的,推测背联两虫的皮层发育既是相对独立的,又有某种机制控制着相互间的协调。背联体棘昆虫在无性生殖周期中总是经历着一个调节成单体的过程,认为这于背联两虫都具有一套结构功能正常的运动胞器(特别是口围带),而产生向不同方向运动的“不协调”的力有关。

Dorsi-connected Stylonychia mytilus (two normal cells connected on dorsal sides) can be obtained by artificial induction, i. e., certain pattern of cutting operation. Results from prolargol staining and scanning electron microscopy (SEM) revealed (hat in each ventral side of the two dorsi-connected component cells, there are ventral ciliaturcs corresponding to a normal S, mytilus. In most cases, on any side of dorsi-connected S. mytilus, there arc 4 rows of dorsal bristles (DB) on the dorsal side of one component cell (arranged similar to lst to 4th DB rows in normal cell), while 2 DB rows (similarly arranged as 5th & 6th rows in normal cell), are on the dorsal side of the other component cell. It is observed that most of dorsi-connected S.mytilus arc formed by the connection of two cells at their dorsal cortical region between their 4th & 5th DB rows. Also, there are cases of various forms of dorsal cortical connections. During asexual division, the morphogenesis of cortical ciliatures on two dorsi-connected cells arc similar to that of normal 5'. mytilus. In both of them, various cortical ciliatures, such as adoral zone of membranclles (AZM), frontal, ventral & transverse cirri (FVTC) , right marginal cirri (RMC), left marginal cirri (LMC) , and DB, are developed synchronously. Thus, it is supposed not only the cortical development in the two dorsi-connected component cells are relatively independent, but, there's also certain mechanism contrplling their mutual coordination. During asexual reproduction, dorsi-eonnected ,S. mytilus are always in the processes of being regulated to normal cells. It is suggested that this is related to the 'un-coord-inated' tendencies toward opposite directions due to the presence of a whole set of locomotive organelles (especially, AZM) with normal structures and functions in each component cell of the dorsi-connected S, mytilus.