598 



ANATOMY OF VERTEBRATES. 



granules and granular corpuscles, more immediately surrounding 

 the germ-cell ; which, moving from the centre to the periphery 

 of the yolk, there forms the ( cicatricula,' the exclusive seat of 

 subsequent developement. In the cartilaginous Fishes the im- 

 pregnating influence is received before the ovum quits the ovarium, 



or shortly after. In the 

 egg's passage through the 

 oviduct the yolk is sur- 

 rounded by fluid albumen, 

 and finally by a case of 

 the denser albuminous 

 secretion of the nida- 

 mental gland. The form 

 of the egg when thus 

 invested is remarkable, 

 and different in different 



genera. 



D 



External form of ova of Oviparous Cartilaginous Fishes. 



cccvin. 



In the Skate, fig. 419, 

 A, it is an oblong quad- 

 rangular flattened case, 

 with the angles produced 

 forward and backward, 

 like those of a butcher's 

 tray. In the Spotted 

 Dog-fish, ib. B, the ova 



O 3 



are also quadrangular, 

 but longer, and the angles 



o J o 



are extended into filamen- 

 tary tendrils, which attach themselves to floating bodies, and thus 

 keep the ovum near the surface, where the influence of solar heat 

 and light is greatest. In Notidanus, with a similarly shaped cirri- 

 gerous egg, the anterior and posterior surfaces are crossed by 

 about twenty parallel transverse ridges. 1 In Cestracion the egg 

 is pyriform, with a broad ridge, or plate, wound edge-wise round 

 it in five spiral volutions. The eggs of Callorhynchus resemble a 

 broad-leaved fucus, in the form of a long depressed ellipse, with 

 a plicated and fringed margin. 2 The ovum of the Myxine 

 glutinosa, fig. 419. c, is a long ellipse, terminated at each end by 

 a tassel of slender tubular filaments, twenty-five to thirty in 

 number, expanding at their free end (opposite D) into a funnel- 

 shaped process. 3 



1 xx. vol. v. p. 70, preps, nos. 3245, 3246. 



2 xx. vol. v. p. 69, preps, nos. 3235, A. and r.. 



3 cccvm. p. 51. 



