FISHES. 37 



and external substance (substantia corticalis and medullaris) does 

 not exist. The entire substance of the kidneys is formed of ccecal 

 tubes which open into the ureters. These usually coalesce in a 

 bladder, or become wider at their inferior extremity. The bladder 

 is situated upon the rectum and the urethra opens behind this 1 . 

 Kenal capsules (renes succenturiati, cctpsulce renales), formerly 

 thought to be absent in fishes, occur in the cartilaginous fishes as 

 narrow, elongated, yellow bands situated on the inner side of the 

 kidneys, and in the bony fishes usually as two small, round, whitish 

 bodies, mostly at the posterior extremity of the kidneys 2 . 



The organs of propagation of fishes are on the whole not very 

 composite. The sexes are always distinct, but often, as in the lower 

 animals, there is a great similarity between the parts that prepare the 

 germ and the seed (ovaries and testes). Sometimes the entire appara- 

 tus of the organs of propagation is limited simply to these indispen- 

 sable and essential parts. Ordinarily there are two ovaries present 

 and two testes ; there are however fishes in which these organs are 

 unpaired, of which the examples are more frequent in female speci- 

 mens. One ovary alone is developed in the perch, in Blennius 

 viviparus, Ammodytes tobianus, Gobitis harbatula, Cobitis tcenia; in 

 many sharks also (Scyllium, Carcharias, Sphyrna, Mustelus and 

 Galeus) only one ovary is present, mostly situated on the right 

 side. In most bony fishes the ovaries form two long and large 

 sacs, which lie on each side near the intestinal canal and the 

 liver (the so-called roe). From the inner surface folds arise which 

 ordinarily form transverse partitions ; in these folds the eggs are 

 developed, which in some fishes are exceedingly numerous in 

 the spawning-season, sometimes some hundreds of thousands. The 

 inferior part of the ovary is without such plates, and serves only for 

 transmitting the eggs ; thus it may be named an oviduct ; and here 



1 See on this subject A. J. D. STEENSTRA TOUSSAINT Commmtatio de systemate 

 uropoetico Piscium, Ann. Acad. Lugd. Bat. 1835. Th e opening of the urethra behind 

 the anus is a special characteristic peculiarity of fishes. From this fact RATHKE and 

 V. BAEB concluded that the kidneys of fishes do not correspond to those of the higher 

 vertebrates, but to the embryonal corpora Wolffiana (the primordial kidneys). In the 

 embryo of fishes at least no corpora Wolffiana, except these kidneys, are met with. 

 H. KATHKE in BURDACH'S Physiologic, n. s. 569 ; V. BAER Entwickelungsgesch. der 



\-Thiere, n. 1837, s. 314. 



2 Comp. STANNIUS in MUELLER'S Archiv, 1839, s - 97 IOI > Taf - 1V - 



