204 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



i uf the body. The head of the worm bores towards the 

 and the epidermis rises up over it as a blister which presently 

 tor mini; a small ulcer with the opening of the burrow in which 

 m lies in its centre. 



If now tin- ulcer comes into contact with cold fresh water the worm 

 ts the muscular wall of its body and forces out a portion of its 

 which immediately bursts and exudes a drop of milky-looking 

 fluid, containing myriads of young worms coiled up in spiral form. 

 larvae measure usually from -5 mm. to -75 mm. in length, are 

 somewhat flattened, and have the hinder 

 end of the body drawn out into a fine 

 point. 



Contact with the water rouses the 

 larvae to activity. They uncoil themselves 

 and swim away rapidly. They are capable 

 ot remaining alive for a period of up to 

 three days but do not proceed with their 

 development unless within that period the}- 

 find their way into the interior of a small 

 fresh-water crustacean Cyclops (Fig. 94). 

 According to the older accounts the young 

 Dracunculus bores its way into the body 

 of the Cyclops between the hard plates 

 covering its abdomen. More recent ob- 

 servers state that it has to be swallowed 

 by the Cyclops, and that within a period 

 of from 6 to 24 hours it has bored its way 

 through the wall of the alimentary canal 

 and taken up its position in the blood- 

 spaces (haemocoele) of the crustacean. 



I"" the body of the Cyclops various changes in detail take place 

 ifn-r alx.ut five weeks the larva is ready for transference to its 



94- 

 Cyclops, 9 containing tun 



host. This takes place apparently by the infected Cyclops 

 Wallowed in drinking water. 



bvioui precaution to take against infection with Dracunculus 



tl'" all drinking water is either filtered, heated, or otherwise 



to destroy the Cyclops. Where the individual is already 



rfidal ulcer should be douched with cold water at in- 



< 2 to 3 weeks-the uterus is completely emptied. The 



*onn may then slowly be drawn out by winding it round 



" ' OT two at a time, or it may be killed in situ by injecting 



