f>40 



ENTOMOSTRACOTJS CRUSTACEA 



-CYCLOPS. 



series, we find layers, sometimes of great extent and thickness, 

 which are almost entirely composed of the Fossilized shells of 

 Cyprides ; whilst in certain parts of the Chalk, which was a Marine 

 deposit, the remains of Bivalve shells resembling those of Cythere 

 present themselves in such abundance as to form a considerable 

 part of its composition. 



499. In the Order Copepoda, there is a jointed Shell forming a 

 kind of Buckler or Carapace that almost entirely encloses the head 

 and thorax, an opening being left beneath, through which the 

 members project; and there are five pairs of Legs, mostly adapted 

 for swimming, the fifth pair, however, being rudimentary in the 

 genus Cyclops, the commonest example of the group. This genus 

 receives its name from possessing only a single Eye, or rather a 

 single cluster of Ocelli; which character, however, it has in com- 

 mon with the two genera already named, as well as with Daphnia 



(§ 500), and 

 Fig. 331. with many other 



Entomostraca. 

 It contains nu- 

 merous species, 

 some of which 

 belong to Fresh 

 water, whilst 

 others are Ma- 

 rine. The Fresh- 

 water species 

 often abound in 

 the muddiest 

 and most stag- 

 nant pools, as 

 well as in the 

 clearest springs; 

 the ordinary 

 water with 

 which London 

 is supplied fre- 

 quently contains 

 large numbers 

 of them. Of 

 the Marine spe- 

 cies, some are 

 to be found in 

 the localities in 

 which the Cy- 

 there is most 



, , „ abundant, whilst 



a, female of Cyclops quadricornis :—a, Body; b, Tail; ^y.^^ i„li«W 



c, Antenna ; d, Antennule ; e, Feet ; /. Plumose seize ^ ners lim aDit 



of tail:— b, Tail, with external egg-sacs :— c, i>, e, f, g, the °P en Ocean, 



successive stage Development of young, and must be 



