106 INVEHTEBRATE ZOOLOGY. 



through the shell, wavmg back and forth, thus beating the gills 

 through the water. There are five pairs of legs, of which the last 

 is placed at some little distance behind the others. The mouth parts 

 consist of a pair of mandibles and two pairs of maxillae, but are too 

 minute for general study, 

 (b) InferiKtl anatomy. The alimentary ca»o7 is somewhat curved, termi- 

 nating in the anal orifice. Where situated ? Two small " livers" or 

 liepatic diverticula lie in the head. Look at these from above. No- 

 tice the color of the food in different parts of the canal. Examine 

 a crushed specimen with high powers and ascertain of what the food 

 consists. In the neck region are a few very delicate wavy tubes, 

 running transverse to the longitiTdinal axis of the body. These form 

 the " shell gland," an excretory organ, consisting of a mass of ne- 

 phridia, which open near the second maxillae. The nervous system 

 consists of a brain lying back of the eye, in the head, connected by 

 commissures to a chain of seven ventral ganglia. Dorsally, at the 

 beginning of the thorax, lies a little oval pulsating organ, the heart. 

 It possesses a pair of lateral ostia for the reception of the blood, 

 which is thence forced outward anteriorly. There are no blood- 

 vessels. The reproductive system is closely connected with organs 

 for the care of the young and the development, and should form 

 the subject of separate investigation. 



78. Specimens may be kept in small aquaria, as in the case of Cyclops. 

 75. Notice the following : — 



(a) Males. These appear only at certain times in the year, the females 



reproducing at other times parthenogeneticallJ^ The testes are sim- 

 ple tubes ventral and parallel to the alimentary canal, tapering pos- 

 teriorly into vasa deferentia, which open ventrally in the abdominal 

 region. The males are best distinguished T)}^ the absence of the 

 brood cavity of the female. 



(b) Females. These are the common form, being often the only sex pres- 



ent in a large aquarium. The ovaries lie in a similar position to the 

 testes. They are nearly transparent, but may be distinguished by 

 large cells, the eggs, which characterize them. The oviducts are at 

 the posterior end of these tubes, but open dorsally into a broad cav- 

 ity, and not ventrally, as in the case of the vasa deferentia. The 

 brood cavity is an oblong space, bounded above and at the sides by 

 the dorsal shell, ventrally by the alimentary canal, and is closed pos- 



