COPEPODA. 



431 



the respiratory function. Circulatory organs are either replaced 

 by the regular oscillations of the intestinal canal (Cyclops^ Achtheres), 

 or there is present in the anterior part of the thorax above the intes- 

 tine (Calanidce) a short saccular heart, which may even be continued 

 into a cephalic artery (Calanella) (fig. 53). 



Generative organs. The Copepoda are of separate sexes. Both 

 kinds of genital organs lie in the cephalothorax and in the thoracic 

 segments, and open right and left on the basal segment of the 

 abdomen. Sexual differences in the form and structure of the 

 different parts of the body are almost uniformly found. These lead 



FIG. 342. Metamorphosis of Cyclops, a, Nauplius larva of Cyclops serrulatus after hatching. 

 b, Older stags strongly magnified, c, Very young Cyclops form. SD, antennal glands ; 

 Ol, upper lip ; Mf, mandibular foot ; Md, mandible ; MX, maxilla, Mxf, maxilliped ; 

 F, F", first and second swimming feet; Ho, urinary concretions; D, intestine; Ad, 

 rectum ; A, anus ; G, rudimentary genital organs. 



in certain parasitic Copepoda (Chondracanthidce, Lernceopodidce) to 

 an extremely striking dimorphism. The males are smaller and 

 move with greater facility ; the anterior antennae and the last pair 

 of feet become accessory copulatory organs, the former serving to 

 hold the female, the latter to affix the spermatophores. The sper- 

 matophores are formed in the vas deferens by a mucous secretion 

 which surrounds the seminal mass and hardens to a tough mem- 

 brane. The females are larger than the males and often move 



