DR. DAVY ON THE TORPEDO. 537 



loped, and being removed when they are tolerably complete. Now it seems more 

 reasonable to suppose that this associated progress of the two is in the relation of 

 cause and effect, than to imagine that the filaments are solely designed as a substi- 

 tute for the branchiae ; especially as the blood in the vessels of the yolk membrane 

 seems to be as well adapted to receive the influence of any little air which may be 

 contained in the fluid in the uterine cavity, as the blood circulating in the vessels of 

 the filaments. 



2. In none of the Squali the foetus of which I have had an opportunity of exa- 

 mining at different periods, have I found the same elaborate apparatus of branchial 

 filaments : they have been less numerous and very much shorter. Does not this 

 greater elaborateness indicate that they are intended, in the Torpedo, for a special 

 purpose ? And when we consider the nature of the electrical organs abounding in 

 fluid, as well as their peculiar office, does it not seem accordant that there should be 

 such a peculiar provision as that in question for their formation ? 



3. In one instance I found a large fasciculus, as represented in Plate XXIV. fig. 2. 

 unconnected with the branchial apertures, attached to the head, anterior to the eyes, 

 in the situation of the principal cluster of mucous glands in the adult fish, between 

 the anterior portions of the two electrical organs. May not this be considered an 

 instantia crucis, both as showing that the branchial filaments are not solely designed 

 as a substitute for the gills, and rendering it highly probable that they are concerned, 

 not only in the development of the electrical organs, but also of the mucous glands ? 



It is not necessary to discuss the other two modes in which the foetus of the Tor- 

 pedo is nourished, analogous to what is witnessed in the chick in ovo, first by means 

 of vessels conveying blood, passing from the yolk membrane, and afterwards, in 

 addition, by the direct passage of the substance of the yolk into the intestine of the 

 foetus, through the vitello-intestinal canal. 



Whether the foetus of those Squali and Rays which are considered ovoviviparous 

 are only nourished in these two ways, or also in the additional manner of the foetus 

 of the Torpedo, is a subject for inquiry. From what I have observed, I am rather 

 disposed to think that they are nourished in the latter manner, though in a less de- 

 gree, and w^ithout excepting even those which are contained in a closed membrane. 



From the facts given in the preceding tables, and from others which I have ob- 

 served, it may be inferred that the Torpedo does not bear young more than once a 

 year ; that the breeding season is the latter end of autumn and the beginning of 

 winter* ; and that the period of utero-gestation is from nine to twelve months -f-. 



I have alluded, some pages back, to the foetal Torpedo at its full term. Since I 



* According to Aristotle, it brings forth in autixmn. In my former paper I supposed erroneously that the 

 principal breeding season is the spring, from the circumstance that the fish at that time abound in ova of a 

 large size. 



t I say from nine to twelve months, because I suspect the period of utero-gestation is not precisely fixed, but 

 that it varies with circumstances favourable or unfavourable to bringing forth. Thus, I have had young Tor- 



