FIG. 335. DIAGRAMS TO ILLUSTRATE THE DEVELOPMENT OF THE CHIEF 

 PRODUCTS OF THE MESODERM. (After J. W. van Wijhe.) 



A and B, transverse sections through an embryo in which the myotomes are 

 beginning to become separated from the middle portions of the mesoderin, 

 which includes the nephrotomes, A being in the pronephric, and B in the 

 mesonephric regions. C, the same, shortly after this separation is completed, 

 and D, later stage, in which the myotomes have extended dorsally and ven- 

 trally so as to surround the body, and have nearly lost their cavities. 



ao, aorta, above which is the notochord, and above this again the medullary cord ; 

 d, intestine ; kd, gonad ; Ih, general coelome ; msc, portion of coslome connect- 

 ing general coelome with its portion in the myotome (myoca-le, myc) ; nt, 

 nephrotome or mesonephric tubule ; p, pronephros ; pg, pronephric or 

 segmental duct ; ski, sclerotome, which gives rise to the skeletogenous layer 

 from which the vertebral column arises ; si, mesenchyme of the lateral plates. 



