206 OUTLINES OF CHORDATE DEVELOPMENT 



male, the sexual cords, after metamorphosis, establish in- 

 timate connections with the cavities of the testis and form 

 the efferent ducts (vasa efferentia) by which the spermatozoa 

 are conducted from the gonad to the gonoduct (vas def- 

 erens). In the female, while the intragonadial portions of 

 the sexual cords may give rise to cavities there, the parts 

 connecting the gonad and the mesonephros undergo degenera- 

 tion and remain vestigial in the adult, forming what is known as 

 Bidder's organ. 



The sexes are morphologically indistinguishable during the 

 early stages of development, and in R. temporaria it is not until 

 the tadpole reaches a length of about 30 mm. (Bouin) that the 

 sex can be distinguished. About this time the ovary acquires 

 a central lumen; the sex cords appear larger in the male, and 

 the form of the nests of germ cells can be distinguished, in that 

 in the testis groups of similar cells are formed while in the ovary 

 the cells become arranged as a follicle surrounding a large cen- 

 tral primitive ovum. 



\ 

 3. The Adrenal Bodies 



The adrenal bodies of the adult frog consist of a thin layer of 

 irregularly distributed tissue on the ventral surface of the pel- 

 vic portion of the mesonephros and intimately connected with 

 it. Histological examination shows that the tissue consists 

 of a coarse network of cell strands with occasional groups of 

 darkly staining " pha?ochrome " tissue. The spaces within this 

 meshwork are occupied by sinusoids of the efferent renal (me- 

 dian posterior cardinal) vein. These two kinds of tissue are 

 known respectively as the cortical and the medullary tissues, 

 not because they have such a relation here, but because the 

 corresponding elements of the adrenals in higher forms have 

 such a disposition. 



The cortical substance of the adrenal appears first, in the 

 larva of about 12 mm. in the form of small cell groups along 

 either side of the wall of the median posterior cardinal vein 

 (Fig. 78, A). They lie below the level of the mesonephroi, and 



