294 FEESH-WATEB AQrAEIA. 



months, and at each laying there would not be less than forty 

 eggs; and from these 320 eggs there would come by the end 

 of a year (supposing, of course, that all were hatched and no 

 enemies attacked the young) 4,442,189,120 Cyclops; that is, 

 considerably more than four thousand millions. As one tries 

 to comprehend this vast number, he need feel no surprise 

 that these crustaceans, notwithstanding their numerous foes, 

 can nearly always be found in such profusion. They supply 

 fish with excellent food, and some authorities say that the 

 trout frequently owes the delicate flavour of its flesh to these 

 little creatures. The young Cyclops is so unlike its parent 

 that it frequently has been mistaken as belonging to a different 

 genus. Dr. Baird considers that it takes these crustaceans 

 from seventeen to twenty days to complete their growth, 

 and during tliis time they moult three times. At every 

 change of shell the little creature becomes more and more 

 like its parent. Cyclops can endure extreme cold much 

 better than drought, for it has been proved that while 

 exclusion from all moisture for five-and-twenty minutes is 

 sufficient to kill them, they will survive continuous freezing 

 for twenty-four hours apparently without any evil conse- 

 quences. The Cyclops feed upon both animal and vegetable 

 matter, but principally the former, and they are most readily 

 kept and bred in confinement. As they not only act the 

 part of efficient scavengers, but also supply the best of 

 living food to fish and the like, they should certainly be 

 encouraged as far as possible in the aquarium. They seem 

 to increase most rapidly in those tanks in which carnivorous 

 animals are kept. They swim in a very jerky fashion. 

 C. quadricornis varies in both size and colour, this variation 

 being chiefly due to locality and food. It is often white, but 

 sometimes of a greenish or reddish tinge. 



Besides the Entomostraca thus briefly described, there are, 

 of course, many others which are just as interesting and 

 nearly as useful in the aquarium. Those just referred to 

 are the commonest and the most easily obtained, and, per- 

 haps, owing to their great prolificacy, the most useful in the 

 tank. 



