ON CRUSTACEA. 
319 
forth in a crowd, pressing one against the other, and after they 
have gone out, the mother closes the ovary. According 
to some writers, these Crustacea are oviparous; but Geoffrey 
appears disposed to believe them oviparous and viviparous ; 
that is, not that the living young are formed in the body of 
the mother, but the eggs ; and instead of excluding these ex- 
ternally, she makes them pass into a sort of membranaceous 
pouch, which she has under the body, that there she hatches 
them, as it were, until these young ones being completely 
formed, issue forth from this pouch. 
The bopyrus cymoihoe , and some others of this order, are 
parasitical. The former inhabit the head of the palcemon 
squilla ; those of the latter genus live altogether at the ex- 
pence of fishes, whose blood they suck. The fish appear not 
to mind them ; but they are not numerous in any individual. 
