INVERTEBRATE ZOOLOGY. 29 



Sub-class I. Entomostraka Small, often mimite Crustacea with a 



variable number of segments (not 20). 

 Abdomen generally without appendages. 

 Naiiplias larva almost universal. Parthe- 

 nogenesis frequent. 



Order 1. Branchiopoda With flat, leaf-like legs bearing gill-sacks. 



Body generally enclosed in an integu- 

 mental duplicature in the form of lat- 

 eral shells or a dorsal shield. 



Sub-order 1. Phijlloi>oda Body plainlj- segmented. Numerous 



pairs of legs (10-40). -^ BrancMpus. 



Sub-order 2. Chidoccra Bodj' enclosed in a shell with two lateral 



valves — head free : second pair of ante- 

 meae enormously develoi)ed, and used as 

 oars. 4-6 pairs of legs. (Jill-sacks may 

 fail. •jfDaphnia. 



Order 2. Copepoda ... .Body generally elongated and plainly 



segmented, v^dthoiit integumental dupli- 

 cature. 4-5 pairs of flattened, two- 

 branched legs used as oars. Eggs in two 

 lateral pedicelled sacks. Many forms re- 

 duced l)y parasitism. 



Sub-order 1. Eiwopcpoda Free-swimming forms with typical char- 

 acteristics. -^ Cyclopia. 



Sub-order 2. Copvjxnla pantsiticd Parasites upon gills of flsh or in 



internal organs. Often with a free-swim- 

 ming stage, especially in male. In later 

 life may be rediiced to a shapeless sack. 

 Antennae may be modified to form 

 hooks, if Lernaect. 



Sub-order 3. BrancJiiitra Flattened oval forms, attached to the 



sides of fish and subsisting upon slime. 

 ifArgnlns. 



Order 3. Ostracoda Body, including head, enclosed in a bi- 

 valve shell, with hinge and adductor 

 muscle, seven pairs of appendages, of 

 which only 2 (or 3) may be reckoned as 

 legs, if Cypris. 



