272 SUPPLEMENT 



to their size. Some of them, closing these fingers with force 

 and rapidity, produce a considerable noise. 



The Crustacea in general, as we have already remarked, 

 live on animal matters, especially on such as are in a state of 

 decomposition. The crabs, craw-fish, and prawns, come 

 from all quarters to the dead bodies which float upon the 

 water, or which are cast out by the sea upon the shore ; and 

 there is every reason to suspect that they are brought thither 

 by the sense of smell. 



It also appears that certain isopods live on the substance of 

 the gelatinous animals, which compose the sponges ; at least 

 it is always on these marine bodies that some of them are to 

 be found in very large numbers. Some others, such as the 

 aselli, &c. are accused of destroying the nets of the fisheimen, 

 by gnawing the ligneous fibres of the cordages with which 

 they are formed. The onisci, or wood-lice, live, as is well 

 known, on rotten vegetable substances. 



Finally, there is no doubt that the smallest entomostraca 

 eat, along with the little animalcule which abound in fresh 

 waters, the remains of vegetables equally microscopic, for 

 their alimentary canal, visible at the middle of their body in 

 consequence of its ti'anspavence, is often of a fine green 

 colour. 



Among the carnivorous Crustacea, there are some which 

 seek a living prey, and fight to procure it. Tn these combats 

 they often lose their forceps, but they shoot out again after a 

 little time. 



Those of the Crustacea whose sexes are separate, never 

 exhibit unions by pairs, which are observed in animals of the 

 first two classes, namely, the mammifera and birds, and which 

 are also to be found again among the insects. In general 

 there is no relation between the sexes but at the period of ' 

 reproduction. 



The females, as we have said, preserve their eggs, after 



