DEVELOPMENT IN ECHIDNA 



23 



to do ontogenetically witli the specific organiza- 

 tion of the manamary apparatus. When closure 

 of the navel opening takes place a part of the 

 body wall in the caudal portion of the incu- 



se " -^"^ "^ \. 



Fig. 8a. 



Fig. 8b 

 Figs. 8a and 8b.— Echidna: Tkansverse Sections 



THROUGH THE PRIMARY- PRIMOEDIA OF A STILL 



Later Embryo (Semon's Embryo) in which the 

 Epidermal Thickening is no longer Apparent, 



AND ONLY THE CUTIS THICKENING IS DISTINCT. 



batorial area remains connected with the bladder 

 by means of the urachus, and is therefore 

 exposed to a continual pull inwards, which is 

 the more efEectual since the muscle-free area 



