EELWORMS. 



71 



for a curious disease in 

 the hop known as " nettle- 

 head " : they are there not 

 as parasites but as sap- 

 rophytes. Fermentations 

 are also produced by some 

 Anguillulidae, such as by 

 the Vinegar- and Paste- 

 worms. By far the greater 

 number live free in damp 

 earth and in water. 



Eelworms are very min- 

 ute worms, with very thia 

 skins, and lay only a few 

 comparatively large eggs, 

 which undergo rapid de- 

 velopment. Parasitic and 

 saprophytic forms can be 

 told by the presence of 

 a curious mouth - spine. 

 This structure, found in 

 the mouth cavity, is very 

 sharp and pointed in 

 front, and can be worked 

 backwards and forwards, 

 so as to penetrate the 

 cell walls of plants. 

 In all cases an eelworm 

 devoid of a spine is not 

 a plant parasite. The 

 most important genera 

 living in plant-tissues are 

 Tylenchus, Aphelenchus, 

 and Heterodera. The for- 

 mer genus also lives 

 the earth and in rootage eraS-ged! 



Fio. 26, — Eelworms (Aru/uillulidce). 

 i, TyleTichus devastatrix, from clover roots ; ii. 

 ovum; iii. anterior extremity; iv. posterior ex- 

 tremity of male. (After Bitsema Bos.) Greatly 



