单环刺螠消化道的发生和分化

用组织学、组织化学和电镜技术对单环刺螠（Urechis unicinctus）消化道的发生及分化进行研究。结果表明，单环刺螠消化道起源于原肠胚期内陷而成的原肠腔；至早期担轮幼虫时期，消化道连通，开始摄食，此时据管腔直径不同消化道可分为口、食道、胃、中肠及后肠。附着变态后，其消化道在结构及功能上都有了明显的发育与分化。至蠕虫状幼虫时期。食道、胃及后肠已出现黏膜下层及肌层。嗉囊与砂囊可明显区分。中肠已产生肌纤维的分化，呼吸肠由中肠分化而来，其胞体细长，且核质比较小，可与中肠明显区分。至幼螠时期，食道前端产生了咽部的分化，至此消化道各部位在结构及功能上都与成体有了很大的相似性。即由口、咽、食道、嗉囊、砂囊、胃、中肠、呼吸肠、后肠和肛门组成。组织化学研究结果表明，随着发育，消化道各部位分别呈现不同的碱性磷酸酶、酸性磷酸酶、脂酶、ATP酶、非特异性酯酶及多糖类物质活性。

Ontogenesis and development of digestive canal in Urechis unicinctus

The ontogenesis and development of digestive canal in Urechis unicinctus was studied using histological,histochemical and transmission electron microscope(TEM) methods in the laboratory.The results showed that,the digestive canal initiated from the gastrocoele,which was formed by invagination at gastrula stage.When the digestive canal opened at early trochophore,the larva began to feed.Here the digestive canal could be divided into mouth,esophagus,stomach,midgut and hindgut according to the canal diameter.After the settlement,the whole canal developed and differentiated evidently.Until the worm-shaped larva,the tela submucosa and tunica muscularis came forth at esophagus,stomach and hindgut.The craw and gizzard could be defined.The muscle fibre could be found in the midgut.The aspiratory intestine could be distinguished from the midgut by the nucleus/cytoplasm ratio.When the larva developed into juvenile,the pharynx differentiated at the anterior part of esophagus,and the whole digestive canal was extremely similar with the adult in the structure and function,consisting of mouth,pharynx,esophagus,craw,gizzard,stomach,midgut,aspiratory intestine and hindgut.Furthermore,in the histochemical study,the different parts of digestive canal showed different activity of nonspecific esterase,alkaline phosphatase,acid phosphatase,ATPase,lipase and polysaccharide.