398 CRUSTACEA ENTOMOSTRACA. 



The alimentary canal is divided into a short narrow oeso- 

 phagus, a wide stomach often with two anterior diverticula, 

 which are sometimes ramified, and an intestine opening in the 

 angle of the caudal fork. Hepatic cells lie in the walls of 

 the stomach, and posterior to these is a tract the cells of 

 which contain urinary secretions. The stomodaeal cuticle 

 only extends over the anterior one-third of the stomach 

 (Hartog). 



Excretory organs. The antennal glands which open at the 

 base of the 2nd antenna of the nauplius are only present in the 

 larva of these as of most other Entomostraca. Glands which also 

 have an excretory function have been found in some genera at 

 the sides of the anterior part of the cephalothorax, and in the 

 Eucopepoda they have been found to open, as usual, on the 

 2nd maxillae (Richard). 



A saccular heart is present in the Calanidae and Pontellidae, 

 but generally a heart is absent, the movement of the blood 

 being effected by the regular oscillations of the intestine. 

 There are no special respiratory organs (unless the lateral pro- 

 cesses of the hind part of the body in the parasitic Pennella are 

 to be so regarded). 



Generative organs. The Copepoda are of separate sexes. In 

 both the generative organs lie in the cephalothorax and the free 

 thoracic segments and open (except in the Choniostomatidae, 

 q.v.) right and left in the basal segment of the abdomen. 

 The males as a rule are smaller and more active than 

 the females. Sexual differences in the form and structure of 

 different parts of the body, such as the modifications in the 

 males of the anterior antennae, maxillipeds or sixth thoracic 

 appendages have been already noted. In the free-swimming 

 genus Copilia (Corycaeidae) the body is cylindrical in the 

 female, flattened in the male. 



But sexual dimorphism of a different nature may also be 

 present to a marked degree. Some species among the 

 pelagic families are beset with setae of such elaborate 

 development and brilliancy of colouring that it appears 

 impossible to regard them as other than ornamental (vide 

 Plates I-IV in Giesbrecht's Pelagischen Copepoden des 

 Golfes von Neapel, Fauna and Flora, vol. xix.). What makes 

 the occurrence of such elaborate ornamentation in this group 



