AND ON THE FOETUS OF THE DELPHINUS NESARNAK. 269 



and condition of the cetaceous parent or dam ; and I shall venture to offer some 

 remarks upon their economical uses or purposes. I believe the observation is new in 

 comparative anatomy and embryology. 



In gestation of the mammifera, the womb expands under a compulsion derived 

 from the augmenting magnitude of the ovum ; which, like an acephalocyst, imbibes 

 the materials or plasma from its placental disc or discs. There is a constant tendency 

 of the fundus and corpus uteri to resist their extension, and an equally constant effort 

 of the cervix and os uteri to retain the ovum within the womb. The proo^ress of a 

 gestation brings that contest to a close by developing the cone of the cervix, and 

 changing it into a cylinder that can no longer counteract the expulsive effort of the 

 fundus. The last conflict is labor, in which the foetus is expelled. 



Thus there is in the gravid womb a facultas retentrix and a facultas expultrix, 

 that are in constant antagonism. 



In the terrestial mammals these forces are balanced according to the genus of the 

 animal, which lives under an ordinary atmospheric pressure of fifteen pounds to the 

 inch. 



Mr. Scoresby in his Account of the Arctic Regions, &c., vol. 2, p. 249, computes 

 the surface of a large whale at 1540 square feet, and he has a foot-note of which the 

 following is a copy. 



" From experiments made with sea- water taken up near Spitzbergen, I find that 

 thirty-five cubical feet weigh a ton. Now, supposing a whale to descend to the depth 

 of 800 fathoms, or 4800 feet, which, I believe, is not uncommon, we have only to 

 divide 4800 feet, the length of the column of water pressing upon the whale, by 35 

 feet, the length of a column of sea-water a foot square weighing a ton, the quotient 

 1371 shows the pressure per square foot upon the whale in tons, which, multiplied 

 by 1540, the number of square feet of surface exposed by the animal, affords a 

 product of 211,200 tons, besides the usual pressure of the atmosphere." 



Mr. S. says that we can have but an imperfect conception of such a degree of 

 pressure, which exceeds in weight, sixty of the largest ships in the British navy, 

 when manned and provisioned and fitted for a six months' cruise. 



Is it not a remarkable thing that the mammiferous cetacea, when launched in the 

 ocean, to be subjected to such inconceivable pressure, should be provided against one 

 of the greatest hazards to which their state as marine mammals could expose them ? 



Seeing the perpetual antagonism of the facultas expultrix and the facultas retentrix 

 in ordinary gestation, it could not happen that the parent should plunge to the depth 

 of even four or five hundred fathoms without losing the fruit of the womb. 



Let it be stated that in any case, as in our specimen, the superficies of the gravid 

 womb is one hundred inches, of which the os uteri has one inch and the rest of the 



