Elinson R P, del Pino E M
J Embryol Exp Morphol. 1985 Dec;90:223-32.
The marsupial frog Gastrotheca riobambae has several reproductive adaptations, most prominent of which is the incubation of the embryo in a pouch on the mother's back. We have followed cleavage and gastrulation by microscopical observation and by vital staining, and have found several alterations in these processes which may reflect the reproductive adaptations. The large, yolky egg has a cap of yolk-poor cytoplasm at the animal pole which is incorporated into a translucent blastocoel roof consisting of a single cell layer. The epithelium of the yolk sac is derived from the roof. The inconspicuous blastoporal lips form near the vegetal pole from cells of the marginal region. Gastrulation movements include the epibolic stretching of the surface towards the blastopore and a contraction of the vegetal surface. The blastoporal lips close over a small archenteron, and the cells of the lips become the embryonic disc, a discrete group of small cells which give rise to most of the embryo's body. The great size difference between animal and vegetal blastomeres during cleavage, the single-celled blastocoel roof, the dissociation in time between archenteron formation and its expansion, the embryonic disc and the slow development distinguish G. riobambae embryos from those of other frogs. The importance of the marginal region which produces the embryonic disc and the unimportance of the most animal region whose fate is primarily yolk sac emphasizes the role of the marginal region in amphibian development.
有袋蛙（Gastrotheca riobambae）具有多种生殖适应性，其中最显著的是胚胎在母亲背部的育儿袋中孵化。我们通过显微镜观察和活体染色追踪了卵裂和原肠胚形成过程，发现这些过程中有一些变化，可能反映了其生殖适应性。大的、富含卵黄的卵在动物极有一层卵黄含量少的细胞质帽，它会融入由单层细胞组成的半透明囊胚腔顶。卵黄囊的上皮细胞来源于这个囊胚腔顶。不明显的胚孔唇在植物极附近由边缘区域的细胞形成。原肠胚形成运动包括表面向胚孔的外包伸展和植物极表面的收缩。胚孔唇在一个小原肠上闭合，唇的细胞变成胚胎盘，这是一组离散的小细胞，发育成胚胎的大部分身体。卵裂期间动物极和植物极卵裂球之间巨大的大小差异、单细胞的囊胚腔顶、原肠形成与其扩张在时间上的分离、胚胎盘以及缓慢的发育，使得有袋蛙胚胎与其他蛙类胚胎不同。产生胚胎盘的边缘区域的重要性以及命运主要是卵黄囊的最靠近动物极区域的不重要性，强调了边缘区域在两栖动物发育中的作用。
