266 SUPPLEMENT 



at first been considered to belong to particular genera, as has 

 been observed in the case of cyclops, whose young, at differ- 

 ent ages, have been named anyone and nauplia, and also in 

 argulus and branchipes. 



These eggs, in one and the same species, are sometimes of 

 two sorts, according to the seasons. Thus the ordinary eggs 

 of daphnis are abundant and naked, while those which are to 

 pass the winter at the bottom of the mud are expelled, only 

 two in number, each enclosed in a capsule, with a double en- 

 velope, and surrounded, moreover, with the membranaceous 

 lining of the dorsal cavity, where they were first deposited. 

 The parietes of this cavity are then thickened and become 

 opake ; and it has appeared to some observers to be affected 

 with a peculiar malady, to which they have given the name of 

 epiiippimn. 



The development of the eggs is more or less prompt, ac- 

 cording to the duration of the life of the species to which they 

 appertain, and the rapidity of their propagation. We have 

 just seen, that in certain genera they are disclosed in the body 

 of the mother. In others, they appear to grow thicker after 

 being laid, before they give birth to the young, and remain in 

 this state many days. There are some, in fine, such as those 

 of apus, which seem capable of being preserved dry for many 

 years, without the gum which they enclose undergoing any 

 alteration ; for, without this supposition, it would be impos- 

 sible, unless we had recourse to the theory of spontaneous 

 generation, to explain the sudden appearance, and in myriads, 

 after heavy rains, of those aquatic flabby Crustacea, which are 

 destitute of all means of transportation, in places where, in 

 the memory of man, they have never been remarked before. 



One of the most remarkable characteristics of the Crustacea 

 is the reproduction of the lost members. The astaci and 

 crabs are subject to lose their feet, which are detached with 

 the greatest facility in the joint? of the articulations. A little 



