170 THE LIFE OF CRUSTACEA 



as in other Cladocera, develop directly, but the 

 resting eggs give rise to larvae of the nauplius type. 



Holopedium, which is found in similar situations, 

 surrounds itself with a mass of a jelly-like substance 

 which it secretes. A similar envelope of jelly is 

 found in some marine plankton animals, though not, 

 so far as is known, in any Crustacea, and it no 

 doubt serves to give buoyancy to the animal. 



The Copepoda of fresh water are as abundant and 

 universally distributed as the Cladocera. Species 

 of the genus Cyclops (see Fig. 14, p. 39), easily 

 recognized by the pear-shaped body and the two 

 egg-packets carried by the female, are to be found in 

 almost every pond and ditch. The genus Cantho- 

 camptus comprises species of smaller size, with 

 slender, flexible body, and carrying only a single 

 egg-packet. The plankton of lakes and ponds 

 includes species of Diaptomus (Fig. 59), which have 

 a narrow body and very long antennules. The latter 

 are held out stiffly while the animal swims by rapid 

 movements of the antennae and mouth parts, making 

 occasional sudden leaps by means of its oar-like feet. 

 In this genus also the egg-packet is single. The 

 development can easily be studied by keeping egg- 

 carrying females of Cyclops in a jar of water, when 

 the nauplius larvae will soon hatch out. 



Although the Copepoda, unlike the Cladocera, are 

 not parthenogenetic, it has been found that certain 

 species of Diaptomus produce resting eggs capable of 



