ARTHROPODA 263 
larva is usually retained, but some forms have in addition a 
compound eye. 
The Ostracoda are dioecious, and the males are easily dis- 
tinguishable from the females; the former usually possess some 
organs for holding the latter; in Cypridina this is found on 
the second antennae, in Cypris on the second maxillae, and they 
Fic. 156.—Transverse section through the body 
and shell of Cypris candida. After Zenker. 
. Shell. 
. Inner fold of mantle lining shell. 
. Ligament between the two halves of the 
shell. 
. Adductor muscle. 
Body. 
. Intestine. 
. Liver tubes extending into the shell. 
. Testes sending prolongations into the shell. 
a pe 
rn or 
“TI 
[o.) 
are also provided with more highly developed sense organs. 
The ovaries and the testes may, like the liver diverticula, 
extend into the lining of the shell (Fig. 156). The accessory 
male organs are very complicated, and the spermatozoa attain 
a great size, being in some cases longer than the body. Cypris 
attaches its ova to water-plants, but Cypridina carries them 
about within the shell of the female until they hatch out. 
OrpDER 3. COPEPODA. 
CHARACTERISTICS.—Lntomostraca with an elongated segmented 
body, without a dorsal shell. The thorax bears four or five 
biramous swimming feet ; the abdomen, which consists of four 
segments, 1s devoid of limbs. Some species are parasitic, and 
are then more or less degenerate. 
An enormous number of very variously modified Crustacea 
are included in the group Copepoda. The free-swimming 
forms are distinguished by the constant number, and by the per- 
sistence, of their paired appendages. The parasitic forms, which 
are very numerous, undergo every stage of degeneration, and in 
the extreme cases lose all trace of their Entomostracan affinities 
in the adult condition. The systematic position of these forms 
is, however, clearly shown by the history of their developement. 
