FORMATION OF PROTECTIVE EMBRYONIC MEMBRANES 



911 



However, in the pig and many other mammals, the allantoic diverticulum is a 

 large, spacious structure (see figure 370D and E). 



Respiratory devices thus arise as diverticula from two general areas of the 

 vertebrate body, viz.: 



(1) the pharyngeal area (see Chapter 14) and 



(2) the hindgut area. 



e. Yolk Stalk, Allantoic Stalk, Belly Stalk, and Umbilical Cord 



As the embryo increases in size (see figures 370C-E; 372B-D), the yolk- 

 sac connection with the mid-gut area of the embryo becomes relatively 

 smaller. The constricted area of entoderm and mesoderm which connects the 

 yolk sac with the midgut is called the vitelline duct or yolk stalk. Similarly, 

 the constricted area of the allantois which connects the allantoic diverticulum 

 with the hindgut area is called the allantoic stalk. As the embryo continues 

 to enlarge, the yolk stalk and allantoic stalk are brought closer together and 

 their mesoderms fuse. The closely associated yolk and allantoic stalks form 

 the belly stalk in the area where they attach to the belly (ventral) wall of the 

 embryo (fig. 370E). The narrowing ring-like area between the ventral body 



Fig. 371. Brood compartments for care of young. (A) Pregnant female of the lizard, 

 Chalcides tridactylus (Seps chalcides), showing uterine compartments containing develop- 

 ing eggs. (Redrawn from Needham, 1942, Biochemistry and Morphogenesis, Cambridge 

 University Press, London.) (B) Dorsal brood pouch in the anuran, Gastrotheca 

 pygmaea. (C) Dorsal brood pouch in Gastrotheca marsupiata. Observe small dorsal 

 opening of pouch. (D) Dissection of vocal (brood) pouch in male of Rhinoderma 

 darwinii. (B-D, redrawn from Noble, 1931, The Biology of the Amphibia, McGraw- 

 Hill, N. Y.) 



