Introduction to A-ni in a I Morphology. 349 



Sub-class 3. Ostracoda (Lafrcille)free, micro- 

 scopic, freshwater, or marine Crustaceans, whose 

 hardened tegumentary 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,f 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 th' <! -position of the hard-shelled win- 



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



abrupt, and the other pointed, with a pedicle attached . 

 an^'lc. 



t In f'ypri> the spermatozoa arc coiled, three times the length of the 

 male animal. 



