M. Coste 071 the Habits of some Marine Animals. 201 



out in irregular plates upon a surface of considerable extent ; in 

 otners, such as the Prawns and Shrimps, the semen is emitted 

 m the form of spermatophora, which are attached to the plas- 

 tron or to the base of the feet of the females. In these species, 

 tJaeretore, the spermatozoids must become disaggregated exter- 

 nally to reach the oviducts, without their being introduced there 

 by the males. But the fecundation is not less ovarian than in 

 the preceduig, although it approaches more nearly to the period 

 ot oviposition. There are even species in which it only precedes 

 the expulsion of the eggs by a few hours. Thus, for example, 

 we have seen a Prawn (Palcemon serratus, Leach) copulate on one 

 day and deposit its eggs on the next. 



As all the Crustacea cany their eggs under the tail, or upon 

 some other part of the body where the incubation takes place 

 and as this nicubation is generally very slow (it does not last 

 less than five or six months in the Lobsters and Palinuri), it 

 tollows that the animals of this class, in casting their shells 

 would have been liable to lose their progeny, unless, by an ad- 

 mirable coinbmation, the periods of the oviposition had not been 

 calculated m relation to those of the moults to which these 'spe- 

 cies are annually subjected until they have acquired their defi- 

 nitive size. Thus, to obtain all the time necessary for incubation 

 nature has chosen that fecundation should take place immediately 

 alter the mothers have thrown off their old skins, in order that 

 the new ones may be a sufficiently lasting protection. 



We have seen a striking proof of this fact in the common 

 bhore Crab and the Prawn of our coasts. The male of the 

 former species selects a female, holds her tightly with the ri-ht 

 loot of the second pair, carries her with him, whether he walks 

 or swims, and seizes her again if they be separated. Some days 

 alter this union, the female, still held by the male, throws off 

 her old covering ; and immediately after this moult is effected, 

 she turns to receive the semen,— an operation which lasts one' 

 two, or three days. ■* 



In the Prawn {Palamon serratus, Leach), the male does not 

 take possession of the female before the moult, as in the com- 

 mon Shore Crab ; but as soon as she has moulted, he pursues 

 her, darts upon her back, clings there, and allows himself to be 

 earned about without making any attempt at copulation as lono- 

 as the female swims ; when she stops, he glides under her by 

 inverting the right side, deposits a double spermatophore upon 

 her plastron in a few seconds, and then resumes his former posi- 

 tion, to recommence the same manoeuvre a moment afterwards. 

 There are some species which have two broods between 

 each moult, and in which the copulation fecundating the first 

 generation appears also to fecundate the second ; of this w 



