86 
OF CARTILAGINOUS fishes. 
dy of the female ; this egg conftfts of two parts, the 
white and red, as in thofe of birds, and inftead of a (hell, 
it is lodged in a cafe formed of a thick tough fubftance, 
refembling a horn that has been foftened in boiling wa- 
ter *. 
The oviparous fifties of this clafs produce their young 
nearly in the fame manner ; inthefe as well as in the vivipa- 
rous kinds, the egg is hatched for fome time in the belly 
of the female, but before the fetus is difengaged from it, 
is excluded from the womb, and left till time and tha 
warmth of the fun bring the inclofed offspring to matu- 
rity. Both differ remarkably from the whales and the 
quadrupeds, wliofe eggs Hart from the ovarium, and enter 
the uterus at the time of conception, where they remain 
only a few days, till they leave that ftate, and are formed 
into a complete fcetns. 
There are other difcrhninating characters belonging to 
this order, lefs difcernible indeed, but fuch as mark a 
difference between them and the adjoining tribes. The 
fpinous fifties we faw had no aparatus for hearing ; it 
is probable, however, that the cartilaginous are furni (ti- 
ed, though imperfectly, with the organs of this fenfe ; 
upon each fide, near the eyes, there is an aperture which 
opens into the mouth, the fuppofed ufe of which is part- 
ly to convey the water into the mouth, which is expel- 
led through the gills, and partly to convey founds to the 
cenforium f . In this refpeft, therefore, the cartilaginous 
fifties may be deemed a more accomplilhed race than ma- 
ny of their companions of the deep. 
The 
Britifh Zoo!. ubi fupra. 
■} Will. Icthyol. Lib lii. p. 45. 
