V NEMATODE PARASITES 203 



in contact with moist soil possibly contaminated with faecal matter. In 

 mines in temperate climates, whither the parasite may be brought by 

 infected immigrants, the chief precaution to be taken to prevent it from 

 establishing itself is strict sanitary control, to avoid the possibility of 

 eggs becoming scattered about the ground in faecal matter : keeping the 

 temperature down below 25° C. by efficient ventilation, and efficient 

 drainage are also when practicable of importance. 



Negator 



Over many parts of Africa, India, the West Indies and the warmer 

 parts of the American continent (extending into the Southern States of 

 North America) there occurs, either alone or associated with Ancylostoma, 

 another Hook-worm which is placed in a distinct genus — Necator. While 

 agreeing with Ancylostoma in the main features of its structure and life- 

 history Necator can be distinguished by certain details. It is slightly 

 smaller ( c? 8 mm., 5 10 mm.) : the head is bent more sharply towards the 

 dorsal side than is the case with Ancylostoma : and the two recurved 

 teeth are replaced by a flat cutting plate (Fig. 92, B) which meets its 

 neighbour in the middle line. 



Dracunculus 



The Guinea Worm — Dracunculus ^ medinensis — is a well - known 

 parasite of man, as well as of the dog and various other mammals, in 

 suitable localities throughout the warmer parts of Africa and Western 

 Asia. It has also been introduced into Fiji and here and there in tropical 

 America. 



The parasite lives in the connective tissue of the host, the male being 

 comparatively small (22 mm., Leiper) but the female reaching a length 

 of up to about 120 cm. with a thickness of a little under 2 mm. The 

 full-sized female, about a year old, is practically filled by the enormously 

 dilated uterus containing millions of eggs, the alimentary canal degener- 

 ating especially in its hinder portion and the anal opening becoming 

 completely occluded. 



After fertilization has taken place the male apparently dies. The 

 female, as the embryos within the eggs develop, slowly migrates towards 

 some portion of the host's skin which is liable to be wet — ordinarily 

 towards the foot or ankle, but in the case of water-carriers accustomed 

 to carry water in skins or other vessels upon their backs or heads towards 



1 Sometimes called by the older name Filaria medinensis. 



