9 8 THE LIFE OF CRUSTACEA 



of minute Crustacea may often be obtained. Numer- 

 ous species of Ostracods, Copepods, and Amphipods, 

 and some Isopods, can be collected in this way, and 

 some of these, at least, show peculiarities of structure 

 which appear to be adapted to a sand-burrowing 

 habit. Perhaps the most remarkable Crustacea 

 living in such situations, however, are the Cumacea. 

 In these, as already mentioned, the gills, which are 

 attached to the first pair of thoracic limbs, lie one 

 on each side of the thorax in a cavity enclosed by 

 the carapace. These cavities are continued forwards 

 to the front of the head, where they unite in a single 

 opening from which a transparent tube (or a pair of 

 tubes) can be protruded. It appears probable that 

 this very peculiar arrangement of the respiratory 

 system is adapted to enable the animals to breathe 

 while buried in sand or mud. The water is probably 

 drawn in behind through the narrow slit between 

 the side-plates of the carapace and the bases of the 

 legs, and is expelled through the tube which is 

 protruded from the front of the head. In this way 

 the delicate gills are protected from injury and kept 

 from becoming clogged with sand, while the effete 

 water, loaded with the products of respiration, is 

 carried off to a safe distance, so that it does not 

 re-enter the gill chamber. 



In the case of such minute forms, however, it is 

 very difficult to determine the precise details of their 

 mode of life by observation of the living animals. In 



