536 DR. DAVr ON THE TORPEDO. 



eluding the weight of the embryo, about 177 grains; whilst the weight of the mature 

 foetal fish is about 479 grains ; proving an augmentation of weight in the mature 

 foetus more than double that of the egg, and in this respect differing remarkably 

 from the foetal chick, which at its full time weighs considerably less than the original 

 yolk and white from which it is formed, owing in part to the evaporation of water 

 through the shell, and in part to the excretions going on, especially of lithic acid 

 derived from the kidneys. 



How is this augmentation of weight to be accounted for ? Is there, as in the ma- 

 jority of the Mammalia, any connexion between the foetus of the Torpedo and the 

 parent through the medium of a vascular and cellular structure ? Or has the foetal 

 fish in utero, like the foetus of the Sepiee in the egg, the power of feeding by the 

 mouth, and of taking food into the stomach ? Or does the uterine cavity of the parent 

 fish secrete or pour out a fluid which is absorbed by and in part nourishes the foetus? 



The first and second query I must answer in the negative. Nothing that I have 

 observed indicates any connexion such as that supposed in the first query, between 

 the parent and foetus. I have carefully examined the gravid uterus under water, 

 thinking it possible that the villi of the uterine cavity might inosculate with the 

 branchial filaments, but I could not detect the slightest union of them, or even ap- 

 position. I have carefully examined, too, the stomach of the foetus in its different 

 stages, and I have always found it empty. Admitting, then, that the augmentation 

 is effected by absorption (the only way apparently remaining to account for it), 

 another question arises, How is the absorption accomplished ? Is the whole surface 

 of the foetus an absorbing surface, as in the instance of some of the Mammalia which 

 are destitute of a placenta, and whose foetus do not appear to be connected with the 

 uterus, as that of the Opossum and Kangaroo ? Or are the branchial filaments the 

 principal absorbing organs ? 



It appears not improbable that both the general surface and the filaments are 

 concerned in the operation. The late Dr. Monro, who observed these filaments in 

 the foetus of the common Skate, supposes that they perform the same function as 

 the gills, and are a substitute for them, like the branchial appendices of the Tadpole; 

 and the same view has been taken by others of analogous filaments belonging to the 

 foetus of most of the Squali. This function they may perform in common with the 

 surface ; and at the same time they may convey nourishment and material for growth. 

 If I may hazard a conjecture, I would suggest that the matter which may be absorbed 

 by the surface, may enter into the composition of the body generally ; whilst that 

 which may be absorbed by the branchial filaments, may be chiefly employed in 

 forming the electrical organs, and perhaps the branchiae and the adjoining mucous 

 glands. I shall notice a few circumstances which appear to me favourable to this 

 conjecture. 



1. The branchial filaments are most numerous and of greatest length whilst the 

 electrical organs are forming, appearing just before these organs begin to be deve- 



