610 THE EMBRYOLOGY OF THE FROG 



extend into the substance of the gonad. In the male, these sexual cords, 

 after metamorphosis, form the vasa efferentia or efferent ducts by which 

 spermatozoa are carried from the gonad proper to the real sperm duct, 

 the vas deferens. In the female, the portions between ovary and meso- 

 nephros degenerate, remaining only as a vestige, called Bidder's organ 

 (Fig. 457). 



The tadpole must be of considerable size before the sexes can be dis- 

 tinguished, Bouin giving the length as thirty millimeters in Rana Tem- 

 poraria. In the male gonad, the cells all look alike, while in the female 

 gonad, the follicle arrangement can be made out, and the ovary acquires 

 a central lumen. 



THE ADRENAL BODIES OR EPINEPHROI 



Figure 351 will show how the adrenal bodies grow on -the meso- 

 nephros of the frog. The important point to remember is that there are 



9*- 



Fig. 351. 



Parts of sections through young R. temporaries, show- 

 ing the origin of the adrenal bodies. A. Through 30 mm. 

 tadpole. B. Through 11 mm. frog after metamorphosis, 

 o, Dorsal aorta ; ac, cortical cells of adrenal body ; am, 

 medullary cells of adrenal body ; ct, connective tissue ; g, 

 gonad ; gs, sympathetic ganglion ; m, mesentery ; n, mesoneph- 

 phros ; rv, revehent renal vein ; v, vena cava ; x, point where 

 ganglion cells enter mesonephros and adrenal body. (After 

 Srdinko.) 



two kinds of cellular substances in these organs. The adrenal bodies lie 

 *rm the ventral surface of the mesonephros in the frog. 



Histologically, one may see a coarse network of cell strands with 

 occasional groups of darkly staining tissue called phaeochrome tissue. 

 Blood from the median posterior cardinal vein occupies the spaces in 

 the adrenal body. The coarse network forms what is called the cortical 

 tissue, and the more darkly staining portions are known as medullary 

 tissue, because in the higher forms of animal life, the darkly staining 

 portion lies toward the inner region of the organ, and the coarse network 

 lies toward the outer or cortical region. 



When the tadpole is about twelve millimeters in length, the cortical 

 region appears as small groups of cells lying along both sides of the 

 wall of the median posterior vein, below the level of the mesonephros, 



