I'C Lessons in Zoology. 



upright, suited to the crevices through which it must 

 often make its way ; while the latter, which burrows in 

 the yielding sand, has a much broader thorax, and can 

 keep its balance in an upright position. Gannmaras, how- 

 ever, must always swim on its side or back. 



The beach-flea has no carapace covering both head and 

 thorax. Remembering that the thorax is that part of the 

 body which bears the legs, we count seven rings of the 

 thorax, each bearing a pair of legs. The first ring of the 

 thorax, that nearest the head, is so small that we must 

 take it on trust, but bears a pair of jaw-feet, nevertheless. 

 The first pair of legs end in rude pincers formed by bend- 

 ing the little hooked claw backward toward the next joint 

 above, which is somewhat broadened. The second pair 

 have larger pincers of the same sort, with the joint above 

 the last much more broadened. The remaining five pairs 

 all end in single claws. The pear-shaped bags at the 

 base of the legs are the gills. 



We are careful to aa; only that we count seven rings of the thorax, 

 for we know it really consists of eight, even if we can see bnt seven. 



The mouth-parts are so tiny that they can scarcely be 

 seen without a magnifying glass. They consist of the 

 pair of jaw-feet already mentioned, two pairs of maxiljse, 

 and one pair of mandibles. The head also bears two 

 pairs of antennae nearly equal in length. 



By placing the head under a magnifier and pressing back the 

 jaw-feet with » pin or a dissecting needle, a carefnl worker may 

 satisfy herself that the hard mandibles and the maxillse, soft and 

 leaf-like, are really present. 



Now taking Orohestia and comparing it with Oammarns, we 

 make the following discoveries : 



The eyes are not on stalks, and are nearly round. 

 The first pair of antennae are very short, indeed. Plates 



