ORDR OSTEACODA ; CYPRIS. 2?3 



aid of a glutinous secretion, an operation which lasts about 

 twelve hours. There are but two pairs of legs in this genus, of 

 which the posterior does not make its appearance outside the 

 shell ; being bent upwards to give support to the ovaries. The 

 food of these little animals consists of dead (but not putrid) ani- 

 mal matter, confervse, &c. ; but they will not attack living animals 

 that are well and strong, although they are often seen to attack 

 worms, &c., when wounded and weak, and even to prey on one 

 another. When the ponds ancf ditches in which they live dry 

 up in summer, they bury themselves in the mud, and thus pre- 

 serve their lives as long as the mud retains any moisture, be- 

 coming as active as ever when the rain falls, and again overflows 

 their habitations. After long-continued droughts, however, when 

 the mud becomes very dry and hard, they perish ; but the race 

 is then kept up by the eggs, which are capable of resisting this 

 influence. These little creatures are very lively ; being almost 

 constantly seen in motion, either swimming by the united action 

 of their antennae or anterior feet, or walking upon plants and 

 other solid bodies floating in the water. When alarmed, they 

 draw their antennae and legs within the shell, and close its valves 

 so firmly, that there is no possibility of opening them. An allied 

 genus, CythermOj distinguished by the possession of three pairs 

 of legs, is an inhabitant of salt water. 



884. There is abundant evidence of the former existence of 

 the minute Crustacea of this group, to an enormous extent ; and 

 their size was much greater. The largest existing species of 

 Cypris does not exceed one-sixteenth of a line in length. But 

 in certain strata of the Secondary and Tertiary formations, which 

 appear to have been deposited by fresh water, we find layers, 

 sometimes of great extent and thickness, which are almost en- 

 tirely composed of the fossilized shells of Cyprides, many of them 

 exceeding a line in length ; and in the Chalk, which was a marine 

 deposit, the remains of bivalve Crustacean shells are frequently 

 to be found in great abundance. 



