PBESH-WATEK CETJSTACEANS. 291 



trouble of procuring, for its interesting habits will be more 

 easily observed than those of its commoner relative, D. Pulex. 

 The Spineless Water-flea (D. Vetula) is without the tail-like 

 spine which is possessed by all the species just mentioned. 

 It has also a small head and hardly any " beak." This creature 

 is fairly common. The Reticulated Water-flea {D. reticulata), 

 as its speciflc name implies, has its shell covered with 

 a net-work, the mesh of which is hexagonal. The spine is 

 short, and is inclined backwards. This animal is by no means 

 rare. The Rounded Water-flea (D. rotunda) receives its 

 name from the fact that its shell is almost circular. It is 

 not uncommon. The Long-spined Water-flea (D. mucronata) 

 may be readily recognised by the straight edge of the front 

 part of its shell and by its long, pointed spine. The whole 

 creature is of a dark grey colour. The different species of 

 these Water-fleas may be easily identified; and they can all 

 be readily kept and bred in captivity. The vessels in which 

 they are confined should possess plenty of vegetation, and 

 ought to be placed in a light position, but not within reach 

 of the rays of the sun. Water-fleas wiU give no trouble at 

 aU, and will be both very interesting and very useful to 

 those who care for and keep aquaria. 



The small and active crustaceans known as CypridcB are 

 placed in the order Ostracoda (from the Greek ostrakon, 

 "a shell," their bodies being inclosed in a bivalve shell). 

 Indeed, their outward appearance is so like very tiny bivalve 

 molluscs that they have been mistaken, when at rest, for 

 young mussels. The Cypridce are divided into the two genera 

 Cypris and Candona. The former genus contains about 

 seventeen different species, aU the members of which are rapid 

 swimmers ; and the latter not more than six, aU of which spend 

 their time in crawling over the mud or weeds of the water 

 in which they live : they cannot swim, because they lack the 

 hairy antenna which their near relatives possess. The Cypridm 

 have two pairs of feet, two pairs of antennae, and one eye. 

 They ai-e found in almost every piece of clear stagnant water, 

 where they' may be easily seen vdth the naked eye. They live 

 chiefly upon dead — not putrid — animal matter, and they lay 



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