744 



FRESH-WATER BIOLOGY 



The fifth feet in Cyclops are very rudimentary structures. 



In Diaptomus the fifth feet take on interesting forms. In the 

 female they are symmetrical, but not so well developed as the 

 preceding swimming feet. But in the male, the right fifth foot 

 differs from the left, and is modified so as to make a grasping 

 organ. The figures in the synoptical key show the form of these 

 appendages. The modifications are constant in a given species, 

 so that the fifth feet in this genus furnish the most important 

 means of specific identification. 



In Epischura the fifth feet are modified more profoundly, and 

 this modification is accompanied by a pecuHar development of the 

 segments of the abdomen, which also serves as a grasping organ. 



Fig. 1172. Nauplius of Cyc/o/)^. The 

 fourth pair of appendages are repre- 

 sented by two setae. (After Glaus.) 



Fig. 1173. Second Stage of Cydo/'^, in 

 which are seen four pairs of appen- 

 dages. (After Claus.) 



In their growth from the egg up, the Copepoda pass through a 

 compHcated series of forms. On issuing from the egg the young 

 animal is a flat, oval creature, without any division of the body 

 into cephalothorax and abdomen, and with only three pairs of 

 appendages, the first three of the mature animal, namely, the first 

 and second antennae and the mandibles. These are all used, in 

 this stage of the animal, as swimming organs. This is known as 

 the nauplius stage (Fig. 11 72). A series of molts follows. In the 



