590 



AMNIOTA. 



rudimentary peritoneal funnel. In the Duck the attachment of the inter- 

 mediate cell mass to the peritoneal epithelium is prolonged further back 

 than in the Chick. 



In the foremost segmental tubes, which never reach a very com))lete 

 development, the peritoneal funnels widen considerably, while at the same 

 time they acquire a distinct lumen. The section of the tube adjoining 

 the wide peritoneal funnel becomes partially iuvaginated by the formation 

 of a glomerulus, and this glomerulus soon grows to such an extent as to 

 project through the |)eritoneal funnel, the neck of which it completely 

 tills, into the body cavity (fig. 403, yl). There is thus formed a series of 

 free peritoneal glomeruli belonging to the anterior Wolffian tubuli '. These 

 tubuli become however early aborted. 



In the case of the remaining tubules develo{)ed from the S-shaped cords 

 the attachment to the peritoneal epithelium is very s()<m lost. The cords 

 acquire a lumen, and open into tlie segmental duct. Their blind extremi- 

 ties constitute the rudiments of Malpighian bodies. 



In the posterior part of the Wolffian body of the Chick the inter- 

 mediate cell mass becomes very early detached from the peritoneal epi- 

 thelium, and at a considerably later period breaks up into oval vesicles 



Fig. 402. Teansvekse section through the trunk of a Duck embryo with 



ABOUT twenty-four MESOBLASTIC SOMITES. 



am. amnion ; so. somatopleure ; sp. spJanchnopleure ; wd. Wolffian duct ; rd. seg- 

 mental tube; ca.v. cardinal vein; vi.s. muscle-plate; sp.g. spinal ganglion; sp.c. spinal 

 cord; ch. notochord; ao. aorta; hy. hypoblast. 



1 These external glomeruli were originally mistaken by me (No. 530) for the 

 glomerulus of the pronephros, from their resemblance to the glomerulus of the 

 Amphibian pronephros. Their true meaning was made out by Sedgwick (No. 550). 



