2 2 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



Sub-type II. ARTHROPODA. . . More specialized Articulates with 



jointed appendages {meropodid) and 

 with somites grouped to form three 

 somite-complexes, head, thorax, 

 and abdomen. These may be dis- 

 tinct or fused, either as cephalo- 

 thorax and abdomen or as a single 

 piece. Internally the cavities of 

 the somites are confluent, without 

 dissepiments. 



Class I. CRUSTACEA Aquatic Arthropods, with two 



pairs of antennae and numerous 

 pairs of appendages, usually show- 

 ing much differentiation. Respira- 

 tion either through the general sur- 

 face of the body or by localized 

 thin places, in the form of plates 

 or dendritic structures, upon or 

 near some of the appendages. A 

 few are secondarily adapted to a 

 terrestrial life. 



Sub-class I. Ehtomostraea Small, often minute Crustacea with 



a variable number of somites. 

 Abdomen generally without ap- 

 pendages. 

 Order i. Phyllopoda Numerous (10-40) pairs of flat- 

 tened, leaf-like legs, bearing sac- 

 shaped gills. X Branchipus. 



Order 2. Cladocera Body enclosed in lateral integu- 



mental duplicatures, forming a two- 

 valved shell which usually covers 

 thoracic and abdominal regions, 

 but leaves the head free. Second 

 pair of antennae enormously devel- 

 oped and used as oar-like organs 

 of locomotion. x Daphnia. 



Order 3. Copepoda Body generally elongated and with- 



