196 ZOOLOGY 



SECT. 



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

 are probably passed through vasa efferentia into the vas deferens, 

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

 considerable size, commonly termed the epididymis, closely applied 

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

 sperms become aggregated into sp&rmatopkoresm 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 vesicula seminalis (v. sem.) imperfectly divided into 

 compartments by transverse partitions (7?) 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 (11. g. $.). The vestigial 

 Mullerian ducts (mul. 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 ccelome, 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, flat 

 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 (br. f.j projecting 

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

 lobed and nearly sessile yolk-sac (yk. 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 

 Squaloraja, 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 " Fishes, 

 such as the Sturgeon, Bony Pike (Lepidosteus), and Bow-fin (Amia) 

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

 distinguished from Elasmobranchs and Holocephali by having the 

 primary skull and shoulder-girdle complicated by the addition of 

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

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



