504 DR DAVY’S FRAGMENTARY NOTES ON THE 
passing into the uterine cavity, and there undergoing its full development, unin- 
closed in any shell or membrane. 2dly, The ovo-viviparous fish, such as the S. 
acanthias, S. galeus, and probably S. carcharias, the ova of which, enveloped in 
a glairy white and contained in a delicate membrane, undergo their development 
in the same cavity. -.3dly, The oviparous fish, such as the S. canicula, R. aquila, 
the ova of which, provided with a horny shell the matter of which is secreted by 
one or more glands, are expelled from the oviducts efor their development 
begins, and are hatched in the sea. 
As regards the first division, are not the ova fully formed in the ovaries, and 
undergo no further increase of size after entering the oviducts? Also, as regards 
the foetus, is not its growth in the uterine cavity not solely due to matter 
derived from the yolk, but in part to matter absorbed from the cavity itself? I 
am induced to suppose that this is the fact, from the analogy of the foetal 
torpedo, which, at its full time of birth, I have found to be very much heavier 
than the egg ;* and also from the circumstance that the uterine cavity, as I have 
seen both in the instance of the Torpedo and of the Squatina, has become much 
thinner as the period of gestation advanced and approached its maturity, com- 
paring it with the average of the organ earlier. 
As regards the second, is not the common including membrane or capsule of 
the ovum and embryo found in the uterine cavity as a temporary provisional 
membrane ? and is it not absorbed, in part or in whole, before the young fish 
quit the uterine cavity? Some of the appearances described under the head of 
S. acanthias and S. carcharias seem difficult of explanation except on this idea. 
The absorption of the membrane, whilst it may conduce to the exit of the young, 
may aid also their growth. 
Further, are not what I have called “ placentze’”’—the cotyledons of MuLLER— 
residual masses of vitelline vessels,—residuary after the absorption of the yolk,— 
the view long ago entertained by a distinguished naturalist ’?}+ and, though dif- 
ferent from true placenta, yet do they not exercise a similar function, suppos- 
ing, as I believe was the case, that in the instance of the young of the Carcharias 
there was an active circulation in the mass, owing to which the~foetus that had 
not the vascular mass detached from it lived so long ? 
As regards the third, are not the ova of these fish all hatched in the sea, their 
development altogether taking place after being laid? That they are, I have been 
led to believe, not so much from my own limited observations of a negative kind, 
never having, in the examination of the eggs whilst in the oviducts, seen any 
* See Physiol. and Anat. Res., vol. i. p. 65. 
+ See Hist. Nat. des Poissons, par MM. Cuvier et Valenciennes, The remains of the vitellus is 
described by the former (inferring that the first volume was written by Cuvier) as adhering to the 
uterus almost as firmly as a placenta. This I have never witnessed; nor have I ever witnessed, till 
at an advanced period, the interior lobe of the vitellus, which is described by him as always existing 
in the foetus,—‘‘ comme un appendice de l’intestin.”—See loc. cit. 

