THE JOINTED-FOOT ANIMALS 



149 



the individuals in the water to which salt had been added 

 were of the form of a species hitherto supposed to be dis- 

 tinct, and bearing a different specific name. The individuals 

 in the water which had been gradually diluted approached 

 the form of an allied genus. Thus a mere chang'e of the 

 amount of salt in solution seems to have been responsible 

 for the different forms assumed by the descendants of the 

 same race. 



Cyclops. Any fresh-water pond will afford millions of the 

 genus Cy'clops (Fig. 75), and the sea contains species of the 

 same genus in such numbers that they 

 with allied genera form a large part of the 

 food of many fishes, and even some species 

 of whales find in them an abundant food- 

 supply. Their powers of reproduction are 

 so enormous that it has been estimated that 

 the descendants of one Cyclops may num- 

 ber, in one year, 4,500,000,000 individuals. 

 Though microscopic in detailed structure, 

 on close observation it is easy to see them 

 darting spasmodically through the water 

 in aquaria. A single compound eye in the 

 middle of the head gives them their name, 

 in reference to the race of mythical giants 

 of Sicily. Two pairs of antennae, used in FlG - 

 locomotion, extend from the front of the 

 head. The legs are two-branched append- 

 ages, also used in swimming. One pair of antennse and 

 the legs are not shown in the figure. Two long appendages 

 extend from the end of the abdomen. The body consists 

 of fifteen somites, five in each of the three regions, head, 

 thorax, and abdomen. The female, in the summer season, car- 

 ries about with her two large brood-sacs of eggs which exten'd 

 diagonally out behind. 



5. Cyclops. 

 Much enlarged. 

 (After Claus) 



