140 M. A. Giard on the Genus Entoniscus. 



moment of its exclusion ; but the size of the eggs which I 

 have found attached to the feet of our sand-flea has taught me 

 that the young of this latter must be of a size greatly superior 

 to that of the insect which I have described and drawn issuing 

 from the ovaries contained within the body of the crabs. 



" Now in what way does the mother Oniscus introduce her 

 brood into the body of the crabs, when this body is completely 

 defended by a hard and crustaceous skin ? Here I must 

 argue by conjecture, but by necessary conjecture, until it may 

 be possible to obtain ocular proof of the fact of this penetra- 

 tion. We have already described above the two cavities 

 situated one upon each side of the body of the crab, and in 

 which the branchise move. The water enters and issues from 

 these by two apertures provided with valves, and situated at 

 the sides of the mouth in front of the lateral commissure of 

 the upper portion with the lower portion of the carapace. The 

 anterior part of these cavities is formed of a delicate mem- 

 brane which clothes the viscera of the crab. We can therefore 

 understand with the greatest facility that the mother insect 

 penetrates with the water into such a cavity, and, perforating 

 its delicate wall, introduces her brood into the body of the 

 crab ; the mother insect enters then in the same manner as 

 the ova of Serpulce or of oysters, which I have frequently 

 found hatched or fixed against the ribs which exist in the 

 above-mentioned branchial cavity. 



" We have, therefore, in the crabs two cases of grafting of 

 animal parts ; the brood of these two insects, which need for 

 their development juices elaborated in an animal body, could 

 not be brought to its term by the mother. Nature has taken 

 upon herself to furnish it with a fat and devoted nurse, 

 namely the body of our crabs. The mother makes a small 

 aperture in the skin which covers the intestine; sometimes 

 she fixes her brood to the outside, sometimes introduces it into 

 the body of the crab, enclosed in a membrane performing 

 the part of a placenta ; and, as the eggs contained in this 

 membrane are animated and tend to develop themselves, it is 

 certain that the canals of this ovary are suckers absorbing the 

 liquids of the vessels of the living crab. By inosculating 

 with these latter and forming anastomoses with them, they 

 constitute a system continuous between the living body of the 

 crab, and another body, likewise living, which tends to com- 

 plete its evolution. In point of fact, a foreign foetus has 

 become the actual progeny of the crustacean, and has deve- 

 loped itself upon this animal in the same fashion as, among 

 the Mammalia, the abdominal foetuses are developed nearly as 

 they would be in the uterus, which is their normal and true 



