SEXUAL ORGANS. 257 



other respects very elongated, the oviducts tortuous, and thus these 

 structures approximate those in the Ichthyic reptiles. 



In Amphioxus we find, in the bladder-shaped ovaries that are 

 situated against the sides of the body, vitelline spheres with distinct 

 germinal vesicles and a single germinal spot. 



The Male sexual organs of the Bony Fishes exhibit the same sim- 

 plicity and type of structure as the female. The testes are sacs, 

 mostly retained in place by mesentery, which, when in a turgid state, 

 like the ovaries, frequently occupy the whole length of the ventral 

 cavity. They are continued to form the seminal ducts, which soon 

 uuite into a short and common excretory duct behind the anus, where 

 they frequently open upon a perforated conical projection or penis. 

 The two testes are not always symmetrical ; the right being often 

 the largest, in others the left. In most of those fishes where the 

 ovary is single, the testicle is also found under similar conditions ; 

 its division, however, into two halves is usually indicated. In Cobitis 

 barbatula, however, the testicle is double though ihe ovary is single. 

 The testicle is frequently plaited like a frill, as in the Eels and Pe- 

 tromyzon, and granular in texture ; while in the Osseous Fishes it 

 usually consists of slender caecal tubes, that are occasionally subdi- 

 vided. A glandular layer, that may be compared to the prostate, is 

 very often developed, e. g. in Gobius and Blennius, at the end of the 

 seminal duct. Conical and often elongated structures, resembling 

 intromittent organs, are found in Syngnathus, Gobius, Lepadogaster, 

 Blennius, and also Petromyzon. In the male species of Sturgeon 

 we find similar infundibula to those of the female opening into the 

 ureters. 



Another type of structure for the male organs is furnished by the 

 Rays and Sharks, and Jjie structure, for example, of their testicles is 

 of very great interest as regards the development of the spermatozoa. 

 The structure of these glands, and their connexion with the epi- 

 didymides, are best seen in the Thorny Rays (Acanthias). The testes 

 consist of white, mostly reniform lobules, which present their con- 

 vex edge externally. Within these lobules we may detect even with 

 the naked eye a granular structure ; the granules are round capsules 

 about one fifth of a line in size, and contain the seminal animalcules 

 in their interior. These spermatozoa are lodged, as in the other 

 Plagiostomi, e. g. Raia oxyrhynchus, in very neat and regular parcels 

 within the capsules. The spermatozoa are absent in the youngest 

 or smaller capsules, which merely contain granular matter, and are 



17 



