480 DEVELOPMENT OF ELASMOBRANCH FISHES. 



ject of some investigations by Dr Meyer 1 and by myself 2 . Their 

 older literature is fully given by Professor Semper. In addition 

 to the above-cited works, there is one other paper by Dr Spengel 3 

 on the Urinogenital System of Amphibians, to which reference 

 will frequently be made in the sequel, and which, though only 

 indirectly connected with the subject of this chapter, deserves 

 special mention both on account of the accuracy of the investi- 

 gations of which it forms the record, and of the novel light 

 which it throws on many of the problems of the constitution of 

 the urinogenital system of Vertebrates. 



Excretory organs and genital ducts in the adult. 



The kidneys of Scyllium canicula are paired bodies in con- 

 tact along the median line. They are situated on the dorsal 

 wall of the abdominal cavity, and extend from close to the 

 diaphragm to a point a short way behind the anus. Externally, 

 each appears as a single gland, but by the arrangement of its 

 ducts may be divided into two distinct parts, an anterior and a 

 posterior. The former will be spoken of as the Wolffian body, 

 and the latter as the kidney, from their respective homology 

 with the glands so named in higher Vertebrates. The grounds 

 for these determinations have already been fully dealt with both 

 by Semper 4 and by myself. 



Externally both the Wolffian body and the kidney are more 

 or less clearly divided into segments, and though the breadth of 

 both glands as viewed from the ventral surface is fairly uniform, 

 yet the hinder part of the kidney is very much thicker and 

 bulkier than the anterior part and than the whole of the Wolffian 

 body. In both sexes the Wolffian body is rather longer than 

 the kidney proper. Thus in a male example, 33 centimetres 



1 Sitzungsberichte d. Naturfor. Ges. Leipzig, 1875. No. 2. 



2 " Preliminary account of the development of Elasmobranch Fishes," Quarterly 

 Journal of Microscopical Science, 1874. "Origin and History of the Urinogenital 

 Organs of Vertebrates," Journal of Anat. and Physiol. Vol. X. 



3 Arbeiten, Semper, Vol. in. 



4 Though Professor Semper has come to the same conclusion as myself with 

 respect to these homologies, yet he calls the Wolfnan body Leydig's gland after its 

 distinguished discoverer, and its duct Leydig's duct. 



