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 GeofFroy 

 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 hopyrus cymotlioe, and some others of this order, are 

 parasitical. The former inhabit the head of the paloemon 

 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. 



