534 



DR. DAVY ON THE TORPEDO. 



the case with the foetus of some of the Squali *. Neither have I found any fluid in 

 the uterine cavity at any period, excepting that already mentioned -j-. 



The facts I have stated relative to the development of the foetus of the Tor- 

 pedo, though amply sufficient to demonstrate that this fish is not oviparous, are 

 not incompatible with its being ovoviviparous, as it is considered by the naturalists 

 who have paid most attention to the subject ; yet I believe it is not strictly so, and 

 that it is more correct to say that it is intermediate between ovoviviparous and 

 viviparous, the foetus, as I believe, deriving its support in part from the ovum, and 

 in part from the parent. The principal fact on which I found this belief is, that the 

 mature foetus is very much heavier than the egg. In the three following Tables I 

 shall give the statical results substantiating this fact. 



The first Table will relate to the ovum just after it has entered the uterine cavity, 

 or before the appearance of the embryo ; the second, to the ovum after the foetal 

 development has commenced, but has made little progress ; and the third, to the 

 foetus when mature, or nearly mature, indicated by the total disappearance of the 

 external yolk, or its being reduced externally to a very small bulk. In noticing the 

 kind of Torpedo, I shall use the popular names by which they are designated at 

 Rome, reserving for another place the consideration of its species. The exact time 

 when the fish was caught will be given, with a view to endeavour to determine its 

 breeding season and period of utero-gestation. 



Table I. 



* The foetus of the Squalus Acanthias, at a very early period, is contained in a delicate membrane, which at a 

 more advanced period, near the full time, disappears. The fcetus of the Squalus Squatina seems to be analogous to 

 that of the Torpedo without a membrane ; that of the Squalus galeus has a membrane, even in its advanced stage, 

 appearing to be, as it were, a link between the Torpedo and the oviparous Rays, whose eggs, inclosed in a thick 

 strong horny shell {Mus marinus, Pulvinar marinum of the older naturalists), are hatched out of the body. 



1 1 have in vain sought in the uterine cavity of the Torpedo for lithic acid, which is so abundantly secreted 



