312 



PILARIS AND THEIR ALLIES 



may attain a length of four feet or more, though the average 

 length is about three feet, while the diameter is less than iV of an 

 inch. The body is smooth, cj^lindrical and milky-white in color^ 

 with the tip of the tail sharply hooked. The male worms are 

 believed to be much smaller than the females. When ready to 

 bring forth her young, the guinea-worm is instinct ivelj^ at- 

 tracted to the skin, especially to such parts as are likely to, or 

 frequently do, come in contact with cold water, such as the 

 arms of women who wash clothes at a river's brink, or the legs 

 and backs of water-carriers. The worm pierces the lower layers 

 of the skin with the front end of her body and the outer layers 

 of the skin form a blister over the injured spot. The blister 



eventually breaks, revealing a 

 shallow ulcer, about as large 

 as a dime, with a tiny hole in 

 the center. When the ulcer is 

 douched with water a milky 

 fluid is exuded directly from 

 the hole or from a very deli- 

 cate, transparent projected 

 structure which is a portion 

 of the worm's uterus. This 

 fluid is found to contain hordes 

 of tiny coiled larvae with char- 

 acteristic straight projecting 

 tails. The larva? (Fig. 131) arc 

 from 0.60 to 0.75 mm. (about ^V 

 of an inch) in length. An hour or so later a new washing with cold 

 water will bring forth a fresh ejection of larvae and so on until the 

 supply is exhausted, a little more of the uterus being extruded each 

 time. After each ejection of the larva? the protruded portion of the 

 uterus dries up, thus sealing in the unborn larvae. This process 

 can be looked upon only as a wonderful adaptation for the pres- 

 ervation of the race. As we shall presently see, the tiny larva? 

 utilize various species of Cyclops (Fig. 132), small fresh-water 

 crustaceans, as intermediate hosts. If the larvae were not de- 

 posited in water, or if they were all poured at once into any bit 

 of water with which the skin of the host came in contact, the 

 chance of their reaching a suitable Cyclops would be very small. 

 The result would usually be family suicide and eventually race 



Fig. 131. Cross section of guinea- 

 worm showing uterus filled with em- 

 bryos. X about 30. (After Leuckart.) 



