EMBRYOLOGY AND REPRODUCTION. 



71 



mouth; it is called the Blastopore. The outside is 

 the skin layer or epiblast, of which we spoke in Chapter 

 III., the inside is the stomach layer, or hypoblast, aad 



Fiff. M.—A, Blastospliei'e (of Amphioius) ; B, beginning of the formation 

 of Gastrnla,, by invagination of the endoderm ; C, complete Gastrula. — (From 

 Clans and Sedgwick, after Hatschek.) 



Fig 18. — fi, Blastosphere; b, Gastrula Btasre of a. ielly-fish {jlurfilia aurita) ; ec, 

 Ectoderm ; 0, Blastopore or mouth of gastrula, — (From Glaus and Sedgwick.) 



the middle layer is not developed at this early stage. 

 Sometimes this blastopore becomes the mouth of the 

 adult animal ; sometimes, in higher forms, it undergoes 



