190 ZOOLOGY SECT, xin 



(ts.) are large ovoid bodies trie tubules of which, apparently 

 do not contain 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 spermatophores 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 vesicula seminalis (v. sem.) 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 

 Miillerian 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. 864) 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. The early development resembles that of the Elasmobranchs ; 

 but the yolk becomes divided into nucleated masses which divide 

 into smaller segments, and the smallest break away and become 

 dissolved in a milky nutrient liquid which fills the spaces of the 

 shell : the advanced embryo has elongated gill-filaments (br. /.) 

 projecting through the branchial aperture (and probably serving 

 to absorb the nutriment derived from the yolk), a diphycercal tail, 

 and a curiously lobed and nearly sessile yolk-sac (yk. s.). 



Fossil remains of Holocephali are 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 Potypterus of the Nile. They 



