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 of known forms 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 fromi 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 miuscles are nearly always of the striped formi, their 

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

 sented by spaces (the blood-sinuses), in free comm/Lmication with 

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

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

 Insecta and Arachnida. The Crustacea 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 



