598 



ANATOMY OF VERTEBRATES. 



granules and granular cor]nxscles, 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 

 ^'9 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 diflerent 

 genera. 



In the Skate, fig. 419, 

 A, it is an oblong quad- 

 rangular flattened case, 

 with the angles prodixced 

 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 Ahtidanus, vfith a similarly shaped cirri- 

 gerous egg, the anterior and posterior surfaces are crossed by 

 about twenty parallel transverse ridges.' In Cestracion the egg 

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

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

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

 a plicated and fringed margin.^ The ovum of the Myxinc 

 (jluthwsa, 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.' 



' XX. vol. T. p. 70, preps, nos. 3245, 3246. 



'^ XX. vol. V. p. 69, prcjis, nos. 3235, A. iind is. » cocviir. p. 51. 



External form of ova of Oviparous CartCaginous Fisbeg. 



CCCVIII. 



