CLASS OF CRUSTACEA. 441 



functions. Sometimes there exists at the bottom of the respi- 

 ratory cavity a sort of trough, destined to act as a reservoir 

 for the water required to maintain their branchiae in a moist 

 state ; at other times, we find on the arch of this cavity a 

 spongy membrane, which seems to serve the same purpose. 

 Most of these land crabs live in moist woods, concealing them- 

 selves in holes, which they dig in the soil, but the localities 

 they prefer vary according to the species ; some live in 

 low marshy grounds near the sea; others prefer wooded 

 hills far from the seashore, and at certain epochs these last 

 quit their usual place of abode to reach the sea.* 



The cloportes (Fig. 419) are also terrestrial Crustacea, 

 whose ae'rien respiration is accomplished by means of foliaceous 

 laminae situated under the abdomen, and which, in other 

 animals formed in the same way, perform the functions of 

 branchi. 



Fig. 430. Gecarcin, or Land Crab. 



570. The Crustacea are all oviparous, and the sexes 

 almost always distinct; but some are hermaphrodite. The 

 female may in general be distinguished from the male by the 

 greater size of the abdomen, and after having laid her eggs, 

 she carries them during a certain time suspended under that 

 part of the body, or even enclosed in a sort of pouch formed 

 of appendages belonging to the limbs ; sometimes the young 

 are produced in this pouch, and remain there until they have 

 passed through their first moulting. The young in general 

 do not undergo true metamorphoses. Sometimes, however, 



* Such are the circumstances which render difficult all minute application 

 of the laws regulating the structure and functions of the now existing 

 living world, to the remains we find in past geological epochs. That 

 which seems aquatic may have been terrestrial, and vice versa. Not that 

 anatomy is at all doubtful when fully known, but the soft structure being 

 destroyed, we want a valuable element in the inquiry. R. K. 



