大瓶螺胚胎发育的初步观察

A PRELIMINARY OBSERVATION ON THE EMBRYONIC DEVELOPMENT OF AMPULLARIA GICAS

本文对大瓶螺（Ａｍｐｕｌｌａｒｉａｇｉｇａｓ）的胚胎发育进行了研究。由于大瓶螺卵具钙质卵壳，故采用定时取样，破壳取胚，间断观察的方法。在２５±１℃气温中，胚胎发育从卵产出母体后至孵化需２７４小时，长度增长２２倍。全过程可分为７个时期：卵裂期、囊胚期、原肠期、担轮幼虫期、面盘幼虫期、幼螺形成期和孵化期。对各期的外部形态特征进行了描述，并绘制了各期形态图，还对卵的结构，各期发育时间及胚胎大小变化作了描述。

This paper deals with the embryonic developmeM of A.gigas.Theembryonic development stages were dlscontlnuously observed because of the eggcapsure.The mathod was the fixadate collected specimen and the egg-capsurebroken into spieces to draw out the embryo.In atmospheric temperature at 25±1℃, the embryonic development took 274 hours and the length of embryo increased22 times.According to the external morphology,whole devlopmental course of theembryo can be divided into 7 periods as follows:1.Cleavage period In the early period cleavage follows the spiral molluscanpattern. The polar bodies mark the animal pole of the egg.2. Blastula period There is no morphologically digtinct, but the blastulacavity can been seen on the seching specimen.3. Gastrula period Gastrula can be divided into the earlier stage,middle stageand last stage,but passed epiboly and invagination.4. Trochophore larva period The time is of short duration. The embryo hasapical,metatroch and telotroch.5. Veliger larva period Fifty-two hours later the embryo has become a veliger larva with veliger area. The foot is bilobed, the larval shell has begun to besecreted. The adult tentacle primordia appear.6. Juvenile snail form period The foot can move, eye primordis appear, theshell covers the body or visceral mass. The time is 60% of the embryonic development.7. Hatching Just hatching juvenile snail has two whorl. The larval livercells appear to be red.