PLATE XV 



FIG. i. Section of the ovary of a kitten, injected and stained (hematoxylin-eosin), x 335. 

 Author's collection. 



This figure shows the ovum, with the vitelline membrane, the protoplasm of the vitellus 

 stained rose-color, the germinal vesicle and the germinal spot, surrounded with the cells of the 

 corona radiata. The ovum nearly fills the Graafian follicle. 



FIG. 2. Section of the testicle of the rabbit (hematoxylin-eosin), x 35. Ferguson. 



This figure shows simply the tortuous arrangement of the seminiferous tubes and the inter- 

 stitial tissue. The magnification is not sufficient to show the structures within the tubes. 



FIG. 3. Transverse section of a chick of about 24 hours, near the caudal end, x 50 (picro- 

 carmin). Strauss. 



In the centre above, bounded by the vertebral plates, is the neural groove. The outer, 

 delicate layer is the epiblast. The innermost layer is the hypoblast. The large cavity below is 

 the enteron, finally to be closed over by the abdominal plates. The round body below the 

 neural groove is a section of the notochord. The masses of cells by the sides of the notochord 

 are the primitive somites. The thick layer extending from the somites between the epiblast 

 and the hypoblast is the mesoblast. 



FIG. 4. Transverse section of same chick at about the middle of the abdomen (same tech- 

 nique and magnification). Strauss. 



The neural canal is nearly closed. The epiblast, hypoblast, and somites are as in Fig. 3. 

 The mesoblast has split into the somatopleure above and the splanchnopleure below, enclosing 

 a large cavity, the celom. 



FIG. 5. Transverse section of a chick of about 24 hours, near the head, X 50 (hema- 

 toxylin). Strauss. 



The neural canal is closed over. The epiblast and hypoblast are as in Figs. 3 and 4. 

 By the side of the primitive somite is a smaller mass of cells, the Wolffian duct. The celom is 

 as in Fig. 4. Between the splanchnopleure and the hypoblast is the omphalo-mesenteric vein. 



FIG. 6. Transverse section of a chick of about 48 hours (same technique and magnification 

 as Figs. 3 and 4). Strauss. 



The uppermost layer of cells is the external (false) amnion. The next layer below is the 

 true amnion. The primitive somites have given off externally the muscle-plates. The two aortse 

 lie below the notochord. The Wolffian ducts are external to the aortas and in the same plane. 

 The somatopleure is thickened and curved and gives off the true amnion. The celom lies 

 between the somatopleure and the splanchnopleure. The omphalo-mesenteric veins are better 

 defined than in Fig. 5, especially the vein on the right side of the figure. 



