38 REPORT OF NEW JERSEY STATE MUSEUM. 



Descriptive Account of the Species and their 

 Higher Groups. 



REIvATlONSHIPS. 



The great group or •phylum containing the Arthropoda em- 

 braces the greater number O'f known fornas of Hfe. They are 

 characterized chiefly by the metameric segmentation, more or 

 less perfected bilateral symmetry — the mouth and anus being 

 placed at opposite ends of the elongated body — and a nervous 

 system formed of a brain dorsally and a double ventral chain of 

 ganglia. Each typical segment of the body carries a pair of 

 appendages, which are divided into distinct limb-segments or 

 podomeres, which are separated from one another by movable 

 joints and acted upon by special muscles. These features will 

 serve to distinguish them from the segmented worms. Arthro- 

 pods have further characters in the almost universal absence of 

 cilia, the muscles are nearly always of the striped formi, their 

 spenns mostly non-motile, and the body-cavity is largely repre- 

 sented by spaces (the blood-sinuses), in free commiunication with 

 the circulatory system. The classes oi this phylum usually ad- 

 miitted are five, as the Crustacea, Onychophora, Myriapoda, 

 Insecta and Arachnida. The Ciaistacea include the crabs, lob- 

 sters, shrimps, wood-lice, barnacles, water-fleas, etc. The Ony- 

 chophora are represented by only the curious Peripatus, cater- 

 pillar-like in form. The Myriapoda embrace the centipedes and' 

 millipedes. The Insecta include all true or six-legged arthropods,,, 

 such as cockroaches, locusts, flies, beetles, moths, butterflies, bees,. 

 etc. The Arachnida include the spiders, scorpions, mites, etc. 



Class CRUSTACEA. 



The Crustaceans. 



Body formed of segments, usually very distinct or well de- 

 fined, motile, of considerable hardness, and without so-called 

 internal skeleton. Five anterior segments joined or fused with 



