410 ZOOLOGY FOR MEDICAL STUDENTS chap. 



The spermatozoa pass from the testis through vasa efferentia forming 

 an irregular network into the Malpighian bodies or tubules of the opistho- 

 nephros and thence by the Wolffian duct to the cloaca and exterior. In 

 different members of the Anura there occur interesting differences in the 

 relations of the network of vasa efferentia to the testis and kidney, there ■ 

 being a tendency for the number of vasa efferentia to undergo reduction 

 and for those that persist as well as the tubules with which they com- 

 municate to become shortened and widened so as to make the route of 

 the spermatozoa from testis to Wolffian duct as simple and direct as 

 possible. The final stage of this modification is seen in Discoglossus, in 

 which the testis is continued into the Wolffian duct by a single direct 

 channel which has emancipated itself entirely from the rest of the kidney. 

 The whole type of modification is precisely like that seen in the Lung-fish, 

 with the striking difference that in the Anura the persisting vasa efferentia 

 are at the headward end of the kidney whereas in the Lung-fish they are 

 at the hinder end. 



A conspicuous feature in the dissection of a typical amphibian is due 

 to the fact that the anterior portion of the ovary and testis degenerates 

 and forms a fatty body in which there is stored up, in the form of 

 fat, reserve nourishment to be drawn upon by the functional part of 

 the gonad while it is preparing for the activity of the breeding 

 season. 



In the Amphibians there are to be found for the first time the com- 

 pound organs known as suprarenals. These are slender organs of a bright 

 yellow colour lying along the ventral (Anura) or mesial (Urodela) surface 

 of the opisthonephros. The study of its development shows that the 

 suprarenal is a complex formed by the fusion of two original separate 

 elements. The first of these — ^known as the " medullary substance " in 

 mammalian anatomy — is derived from the sympathetic ganglia and its 

 substance is characterized by taking on a deep yellow or brown colour 

 when treated with salts of chromic acid. The other element — the 

 " cortical substance " of mammalian anatomy — is derived on the other 

 hand from thickenings of the peritoneal epithelium between the two 

 kidneys and is characterized by its cells containing numerous granules 

 of fat-like material. Although the suprarenal complex makes its first 

 appearance in the Amphibians it should be noted that its components 

 are already recognizable as low down the scale as in Elasmobranchs 

 although there they never become united together into a compound 

 organ. 



The suprarenal is an important ductless gland, the " medullary sub- 

 stance " making an important contribution to the internal medium in 



