THE CLASS CRUSTACEA 315 



The nauplius larva is not peculiar to Cyclops, but is 

 characteristic of all the subclasses of the Entomostraca, and 

 may even be said to be characteristic of the Crustacea as a 

 class, since it also crops up among the Malacostraca. 



Cyclops in relation to Guinea-worm. — The adult guinea- 

 worm, of which the female only is certainly known, is a 

 subcutaneous parasite of man in India and South-western 

 Asia, in Tropical Africa, and in certain parts of South America. 

 It is a worm that may attain a length of 6 feet. When 

 ripe it causes the formation of an abscess in the skin of its 

 " host," through which it breaks in order to give birth to its 

 myriad progeny of minute embryos. The escaped embryos, 

 which are about -5 mm. long, if they happen to be washed 

 into a watercourse, attack any convenient species of Cyclops. 

 According to some authorities they bore through the body- 

 wall of the Cyclops, but Leiper thinks that they enter at 

 the mouth. If many embryos attack a single Cyclops the 

 result is fatal; but if only a few enter they, in a term 

 ranging according to temperature from two to eight weeks, 

 undergo a metamorphosis and become quiescent in the 

 living Cyclops. What subsequently happens cannot be 

 certainly affirmed, but it is inferred that if an infected 

 Cyclops happened to be swallowed by a man who is not 

 fastidious about his drinking-water, the quiescent embryo 

 is released when the Cyclops is duly digested, and subse- 

 quently fulfils its destiny as a parasite of its final host. But 

 whether the guinea-worm actually reaches man in the envelope 

 of a Cyclops, or whether, as seems less probable, there is 

 another post-Cyclopean stage, there is no doubt about the 

 necessary intermediation of Cyclops. 



Prophylaxis against guinea-worm seems, therefore, to be 

 entirely a question of scrupulous attention to sources of 

 drinking-water in places where the parasite occurs. Water 

 containing even uninfected Cyclops is certainly not fit to 

 drink ; but if it must perforce be used it should first be 

 boiled. A well known to contain infected Cyclops should (if 

 the populace is sufficiently intelligent not to suspect sinister 

 designs upon life and liberty) be treated with a considerable 

 quantity of quicklime, so as to heat the water suddenly. The 

 well must, of course, be left for a time to recover. 



