Introduction to Animal Morphology. 349. 



Sub-class 3. Ostracoda [Latreille] — free^ micro- 

 scopic, freshwater, or marine Crustaceans, whose 

 hardened tegnmentary folds form a bivalve, ventrally 

 open, shell-like case, closed by an adductor muscle ; 

 they form one family. The body is of a bean-like 

 form, often acardiac, with gills appended to the first 

 and second pair of feet, while the third and fourth 

 have none. The rudimental post-abdomen is un- 

 jointed ; the eyes are two, single or aggregate ; the 

 two pair of tentacles are equal and bristled ; the 

 mandibular palps jointed. There is a crop with a 

 cartilaginous bristled and folded ring around it, and 

 the intestine has a convolution. There are six testi- 

 cular pouches,* ending in a tortuous vas deferens. In 

 the males the third pair of legs form claspers ; the 

 third and fourth pair of abdominal legs are absent in 

 Cypridina ; swimming feet in Cypris,t clawed in 

 Cythere. 



Sub-class 4. Branchiopoda — usually minute, mostly 

 freshwater forms, the direct expansions of the Nauplius 

 type, with 1-3 pairs of jaws, a distinct head, rudi- 

 mental thoracic limbs, but a large abdomen, either 

 homo- or hetero-nomously segmented, bearing 5-60 

 feet ; a heart is always present, and the oesophagus 

 rarely has a crop ; the feet, or some of them, are flat, 

 lobed, with gill appendages ; the eyes are simple or 

 compound, but never with a facetted cornea ; the males 

 are few, often with large spermatozoa, and impregna- 

 tion precedes the deposition of the hard-shelled win- 



* The viviparous Cythere has a lash-like spermatozoon, with one end 

 broad, abrupt, and the other pointed, with a pedicle attached at right 

 angle. 



t In Cypris the spermatozoa ai'e coiled, three times the length of the 

 male animal. 



