GUINEA-WORM IN CYCLOPS 313 



suicide. The repeated birth of a limited number of progeny 

 each time the skin of the host comes in contact with water is 

 therefore a successful solution to a problem which to a blind 

 burrowing unmeditative worm must otherwise present insuper- 

 able difficulties. When 

 all her young have been 

 deposited, under the stim- 

 ulus of contact with water, 

 the parent worm shrivels 

 and dies and is soon ab- 

 sorbed by the tissues on 

 which she formerly preyed 

 and through which she 

 roamed. 



The embryo worms, 

 safely deposited in water, 

 unroll themselves and be- FlG> 132 Cyclops 8pm (?)> some species of 



gin to Swim about in a which serve as intermediate hosts of guinea- 

 P , . i. ,1 worms. X about 25. 



fashion peculiar to them- 

 selves. Their bodies are somewhat flattened and they have a 

 slender tail. They swim by a few quick sculling motions of the 

 tail, followed by a pause, then a few more strokes, etc., in the 

 manner of a tadpole. In turbid water they remain alive for 

 two or three weeks but eventually perish unless they come in con- 

 tact with a Cyclops, into the body of which they make their way. 



They usually enter by way of the mouth, sometimes as many 

 as six or ten entering a single Cyclops. In a day or two they 

 leave the stomach of Cyclops and enter the body cavity. In 

 spite of the relatively large size of the worms the crustaceans 

 seem to feel very little inconvenience, and seldom succumb 

 even to very heavy infection. 



The young guinea-worms become fully developed in Cyclops 

 in from four to six weeks, according to the temperature, mean- 

 while having undergone one and perhaps two moults. They are 

 then about one mm. (-fe of an inch) in length, and ready to in- 

 fect a new host. Entrance to the new host is probably accom- 

 plished by the accidental drinking of a Cyclops with unfiltered 

 water. The female worms become adult in their new host in 

 about a year so the larvae can again be deposited at about the 

 time that Cyclops becomes abundant. 



