Volume 1

The history of British fishes / [Robert Hamilton].

  • Hamilton, Robert, M.D.
Date:
[1876]
Catalogue details

Licence: Public Domain Mark

Credit: The history of British fishes / [Robert Hamilton]. Source: Wellcome Collection.

    72/392 (page 66)
    it may, we have little doubt that in the AnaVeps t^ti'opkthalmus^ one of the family, this peculiarity exists. It is so distinguished by Cuvier : as is also the genus Poecilia^ a confined group of small fishes which inhabit the fresh waters of America (Cuv. & Val., xi. 334); and also the Silures (Ib. i. 3U3), which may therefore be added to the list. Upon the wliole, therefore, this mode of deve- lopment is rare in Osseous fishes, whilst the reverse is the case in Cartilaginous; the sharks and rays, for the most part, belonging to this division. Of the sharks, we name the families Ga^ei, MmteU^ Zyijceni\ Alopccii\ Sjfinaces, Srpnni, and Sgua- t'men; and of the Rays, the families Prisiuks, Bhi- no/>atides', Torpediiies, Tri/yones, Myliohatide^, and Ccphaloptcrcv. The coverings of the ovum in these ovo-viviparous fishes are remarkably thin; and the ova increase in size, as previously hinted, by the absorption of the surrounding fluid, Dr. Davy hav- ing observed that a developed embryo of the Torpedo is much heavier than an undeveloped one. In one instance, before the a])])earance of the embryo, the ovum of a torpedo weighed 132 grains—an ovum, in which the embryo was visible, 177; whilst the weight of the mature fish, previous to birth, was 471) grains; a fact which is important, as it shows ho\> nearly allied arc the viviparous development with- out immediate connexion with the parent, and the viviparous development in which that connexion pul“^ists. The third method of development exists only in