Parker. — On the Gravid Uterus of Mustelus antarcticus. 221 



fore, to call it the pseud-amnion.* The fluid it contains and in which the 

 foetus floats is evidently a serous fluid, and, having the same relations to 

 the foetus as the amniotic fluid of the higher Vertebrata, may be called the 

 pseud-amniotic fluid. 



The outer or vasculan layer of each compartment, formed by the 

 mucous membrane proper, contains the blood-vessels from which the foetus 

 derives its supply of oxygen : it is therefore roughly analogous to the chorion 

 of mammals, and may be called the pseudo- chorion. 



As regards the histology of the membranes, the most important fact is 

 that the pseud-amnion is a true cuticle : it is quite structureless, and is in 

 close contact with the free surface of the mucous membrane, from the epi- 

 thelium of which it is evidently formed as a cuticular secretion. 



As all the specimens I have hitherto examined have been in approxi- 

 mately the same stage of pregnancy, I have been unable to make any 

 observations on the mode of formation of these remarkable membranes : 

 one would be disposed to think, however, from their final disposition, that 

 the investment of each impregnated ovum is formed in much the same way 

 as the human decidua reflexa. 



The pseud-amniotic fluid is colourless, transparent, and very slightly 

 opalescent. Treated with nitric acid, it gives no trace of the xanthoproteic 

 reaction, and may therefore be assumed to contain not more than the merest 

 trace of proteids. Boiled with nitric acid, it gradually assumes a very dark- 

 brown colour. Evaporated to a small bulk and treated with nitric acid, it 

 gives an abundant crop of crystals of urea nitrata, so that it must contain a 

 considerable quantity of urea, indicating an active renal secretion on the 

 part of the foetus. Evaporated to a third of its bulk and treated with 

 hydrochloric acid, it assumes a pink colour, which gradually deepens into 

 dark brownish-red, and deposits a fine pulverulent precipitate of a deep 

 brown colour. Examined under the microscope this deposit shows no trace 

 of uric acid crystal, and appears to consist entirely of fine amorphous 

 granules. I can form no conjecture as to its nature. 



From the arrangement of the foetal membrane of Mustelus antarcticus, it 

 is certain that both pseud-amnion and pseudo-chorion are ruptured at 

 birth, and from this condition at the end of pregnancy, I feel sure that they 

 are entirely thrown off, — in other words that they form a true decidua. From 

 the extraordinary thinness of the muscular layer of the uterus, it is certain 

 that it can be of little or no use in the expulsion of the foetuses : it would 

 seem that they must simply swim into the world, birth being due to the 

 activity not of the mothers but of the offspring. 



* There is hardly likely to be any confusion between this pseud-arnnion and the 

 so-called " false amnion " of Amniota. 



