REMAK 



211 



formed the characteristic proto-vertebral segmentation, the 

 latter split to form the pleuro-peritoneal or body-cavity. 

 Remak describes the latter process as follows : " In the 

 region of the trunk, where a greater independence of the fate 

 of the alimentary canal and its annexes becomes necessary 

 for the voluntary executive organs, the ventral plates undergo 

 a process of splitting, leading to the formation of the sensitive 

 part of the integument (the Hautplatten), the muscular part 

 of the alimentary tube (the Darmfaserplatteti], and the 

 mother-tissue of the generative organs (the Mittelplatteri}. 



FlG. 12. Transverse Section of Chick Embryo. 

 (After Remak.) 



h. Epidermis. 



m. Spinal cord. 



mw. Dorsal plate. 



ug. Pronephric duct. 



pa. Aortic root. 



hp.\ 



and r" Hautplatte." 

 itm. J 



mp. " Mittelplatte." 

 d/. " Darmfaserplatte." 



x. Edge of amniotic fold. 

 ph. Pleuro-peritoneal 

 cavity. 



d. Epithelium of alimen- 

 tary canal. 



From the Hautplatten there develops, without the dorsal 

 plates seeming to take any part in the process, the rudiment 

 of the extremities " (p. 79). 



His Darmfaserplatten form the nervous and muscular 

 tissue of the alimentary canal and its dependencies, and also 

 the heart ; the Hautplatten form the general body-wall 

 (exclusive of the skin) and the appendages. In the embryo 

 they line the amniotic cavity. The skeleton and peripheral 

 nerves originate wholly within the middle layer. 



Remak's conception of the relations of the three germ- 

 layers to one another and to the body-cavity is well illustrated 

 in Fig. 12. 



In his germ-layer theory Remak's standpoint is histo- 



