598 



ANATOMY OF VERTEBRATES. 



419 



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 es? when thus 

 invested is remarkable, 

 and different in different 



genera. 



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 

 are also quadrangular, 

 but longer, and the angles 

 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 Myxinc 

 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. 

 - xx. vol. v. p. 69, preps, nos. 3235, A. and B. 



3 cccvin. p. 51. 



