19fi ZOOLOGY SECT. Mil 



fully developed sperms, but only immature sperm-cells. These latter 

 arc probably passed through vasa efferentia into the vas deferens, 

 Avhich is coiled in a highly complicated manner to form a body of 

 considerable size, commonly termed the epididymis, closely appHed 

 to the surface of the anterior part of tiie kidney. In this the 

 sperms become aggregated into spcrmcdophorcs in the form of small 

 ovoidal capsules surrounded by a resistant membrane and full of a 

 gelatinous substance in which bundles of sperms are imbedded. 

 The lower end of the vas deferens {v. df.) is dilated to form a large 

 cylindrical vcsinda scmincdis {v. son.) imperfectly divided into 

 compartments by transverse partitions {B) and filled with a 

 greenish jelly. The spermatophores {sph) are passed into these 

 compartments and finally make their way through the central 

 passage into the urinogenital sinus {u. g. s.). The vestigial 

 Mlillerian ducts {viul. d.) are much more fully developed than in 

 the Dog-fish: they are complete, though narrow, tubes opening 

 in front by a large common aperture into the coelome, and 

 behind connected with the urinogenital sinus. 



Development. — Internal impregnation takes place, and the 

 oosperm becomes surrounded, as in the Dog-fish, by a horny egg- 

 shell secreted by the shell-glands. The egg-shell of Callorhynchus 

 (Fig. 853) is of extraordinary size — about 25 cm. in length, 

 or fully five-sixths as long as the abdominal cavity — and the 

 elongated chamber for the embryo is surrounded by a broad, fiat 

 expansion covered on one side with yellow hair-like processes, and 

 giving the shell a close resemblance, doubtless protective, to a 

 piece of kelp. Nothing is known of the early development : the 

 advanced embryo has elongated gill-filaments {hr. f.) projecting 

 through the branchial aperture, a diphycercal tail, and a curiously 

 lobed and nearly sessile yolk-sac {^k. s.). 



Fossil remains of Holocephaliare known from the lower Jurassic 

 rocks upwards. . As might be expected, they consist mostly of teeth 

 and of dorsal fin-spines, but in some cases, and notably in 

 Sq;iialon(ja, practically the whole of the skeleton is preserved. 



Sub-Class III.— Teleostomi. 



In this sub-class are included all the commonest and most 

 familiar Fishes, such as the Perch, Pike, Mackerel, Cod, Sole, 

 Herring, Eel, Salmon, etc., as well as the so-called " Ganoid " F'ishes, 

 such as the Sturgeon, Bony Pike (Lrpidodeus), and Bow-fin {ybnia) 

 of North America, and the Folyptcrns of the Nile. They are 

 distinguished from Elasmobranchs and Holocephali by having the 

 primary skull and shoulder-girdle complicated by the addition of 

 nivesting bones, and by possessing bony instead of horn-like fin- 

 rays. The gills arc covered by an operculum ; the anus is distinct 



