S8S NATURAL ARRANGEMENT OF INSECTS. 



and knowing so little as we do of the habits of these crea- 

 tures, they being chiefly natives of the ocean and its 

 recesses, it is, consequently, only from their structural 

 details that they derive an interest. These are as distinc- 

 tively inhabitants of the water as the metamorphotic 

 hexapod Insecta are of the land. Their integument 

 is usually harsh, hard, brittle, and crustaceous ; whence 

 their name : and that which generally covers conjunc- 

 tively the head and thorax, is called, technically, the 

 carapax, or shield. We think this integument cannot 

 be considered thoroughly analogous to the dermo-skele- 

 ton of the hexapod insecta, as it is more independent of 

 muscular attachment. Waiving the difficulties and ques- 

 tion of their preliminary transformations, we find that 

 their growth is subsequently effected by casting their 

 skin, which they, as it were, creep out of ; in which 

 state the animal becomes sickly and seeks solitude. 

 These creatures have two pairs of antennae, and a mouth 

 furnished laterally with numerous appendages. It is 

 sometimes true legs which surround the mouth, and which 

 thus perform the double function of maxillae and legs ; 

 but, in general, many of them are devoted exclusively 

 to the prehension of food ; and, as we descend the 

 series, we observe a proportionate decrease of these 

 appendages, and an r'ncrease of the number of legs : the 

 latter are affixed to the thorax; they generally con- 

 sist of five or seven pairs, and their form varies with their 

 function, whether for the use of swimming, walking, 

 or prehension : in the first case, they are broad 

 and more or less membranous ; in the second, slender 

 and lengthy; and, when formed for prehension, they 

 terminate in a claw. Beyond the legs, and attached to 

 the successive segments of the abdomen, there is a 

 double row of appendages which assist them to swim 

 and to carry their eggs. These few generalities must 

 suffice : of course, great variations and modifications are 

 found ; but the insects themselves take their definite 

 grouping chiefly from the arrangement, disposition, 

 uses, and structure of the legs. They constitute two 

 large divisions, the masticating and suctorial Crustacea, 



