//. TYPES IN DETAIL IVITH THEIR SUBORDINATE GROUPS. 23 



out integumental duplicature. 

 Four to five pairs of flattened, 

 two-branched legs used as oars. 

 Eggs carried in two lateral sacs on 

 the sides of the abdomen. Many 

 forms reduced by parasitism. 



X Cyclops, LerncBa, Argulus. 



Order 4. Ostracoda Body, including head, enclosed in 



a bivalve shell, with hinge and ad- 

 ductor muscle. Seven pairs of ap- 

 pendages, of which only 2 (or 3) 

 may be reckoned as legs. 



X Cypris. 



Order 5. Cirripedia Free-swimming only when young. 



Adults become sessile and are 

 enclosed in an inverted position 

 in a calcareous two-valved shell. 

 Generally six pairs of two- 

 branched legs, modified to form 

 delicate many-jointed cirri. 



X Lepas, Balanus, Sacculina. 

 Sub-class II. MALAKOSTRAKA .... Generally large forms with a con- 

 stant number of somites (20), con- 

 sisting of a head with five, a thorax 

 with eight, and an abdomen with 

 seven somites. The first two por- 

 tions are often fused to form a 

 cephalo-thorax of thirteen somites. 

 Only the first six abdominal so- 

 mites bear appendages, and of 

 these the last pair is generally 

 modified and united with the ter- 

 minal somite to form a caudal 

 appendage. The paired repro- 

 ductive orifices of the male are 

 found upon the last thoracic legs, 

 near the base, and those of the 



