716 



AMNIOTA. 



In the Duck the attachment of the intermediate cell mass to the peritoneal 

 epithelium is prolonged further back than in the Chick. 



In the foremost segmental tubes, which never reach a very complete 

 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 invaginated by the formation of 

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

 through the peritoneal funnel, the neck of which it completely fills, into the 

 body cavity (fig. 403, gl). There is thus formed a series of free peritoneal 

 glomeruli belonging to the anterior Wolfnan tubuli 1 . These tubuli become 

 however early aborted. 



In the case of the remaining tubules developed from the S-shaped cords 

 the attachment to the peritoneal epithelium is very soon lost. The cords 

 acquire a lumen, and open into the segmental duct. Their blind extremities 

 constitute the rudiments of Malpighian bodies. 



am 



FIG. 402. TRANSVERSE SECTION THROUGH THE TRUNK OF A DUCK EMBRYO WITH 



ABOUT TWENTY-FOUR MESOBLASTIC SOMITES. 



am. amnion ; so. somatopleure ; sp. splanchnopleure ; ivd. Wolffian duct ; st. seg- 

 mental tube; ca.v. cardinal vein; m.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. 539) for the 

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

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

 550). 



