148 CRUSTACEANS. 



of the shell, susceptible of great elevation, and of being folded entirely 

 back : that of the male is very narrow, but susceptible of a similar posi- 

 tion. Here are displayed the admirable provisions of Nature. The 

 aprons of both are folded back in the mutual embrace. Under that of the 

 female are now seen two circular orifices, through which the roe, ripening 

 within, escapes to attain maturity without. As it diffuses in vast abun- 

 dance, the apron of the female is gradually and proportionately elevated 

 while covering the encreasing mass of ova. Sometimes it rises so high 

 as to stand vertically or at right angles to the under surface of the shell, 

 if reversed, and then the ova of the common crab are in tens of thousands. 



Here the roe remains in permanent adhesion to the shell ; no part 

 of it is deposited on foreign substances to be hatched, as is the case with 

 many animals insects in particular to which crabs have been com- 

 pared, as if allied. The whole continues attached to the body of the 

 parent, until by supervening maturity, the foetus bursts the egg or cap- 

 sule to escape, the tie seems to be then dissolved for ever. 



Should I not be mistaken, the ova of the whole tribe of Crustacea 

 adhere externally to the lower part of the thorax or abdomen of the 

 females. In a few which naturalists include here, they are discharged 

 through long tubes with the advancing embryo in an envelope. 



I have not been able to ascertain that the young of any species of 

 the Crustaceans are ushered into life under the precise form of the pa- 

 rent. Many undergo a great metamorphosis. In those best known, a 

 much farther development succeeds, as they issue forth, for indiscrimi- 

 nate distribution amidst their boundless element, they readily escape 

 the view of the naturalist. 



The change of some is perhaps inconsiderable, and chiefly limited 

 to the acquisition of additional limbs. Several species of animals now in- 

 corporated with this comprehensive tribe are less distinguished by such pe- 

 culiarities. But the young and the adults of others could not be possibly 

 identified as of the same species, unless bred before the observer's eyes. 



The preservation of living subjects, together with unwearied study, 

 can alone lead to the solution of points so embarrassing. But here we 

 are opposed by the erratic habits of many. Possibly a very small pro- 



