60 



NEMATODE WORMS. 



moults precede the adult stage. The simplest form of develop- 

 ment is where the embryo, enveloped still in its egg-membrane, 

 is transported, passively, in the food to the host (Oxyuris). In 

 the Ascaridm the embryo, which is provided with a boring 

 tooth, may pass sometimes into an intermediate host, by which 

 it is transported with its host in food and water into the second 

 host, where it will become sexually mature. 



The food of Nematodes which are parasitic consists of the 

 organic juices of the body. They nearly all seem to lead a free 

 life during some period of their existence. Tho.^e that are 



Fig, 18.— Anguillulid^ (Eelworms). 



Li, Mature 9 with oral spine ; & and c, ova ; d, extremity' of £ ; e, anterior of adult. 

 (Enlarged, after Ritsema Bos.) 



parasitic in plants, causing such diseases as clover-sickness, ear- 

 cocldes or purples in corn, &c., are called eelworms. Many of 

 these eelworms, however, only live in decaying parts of plants, 

 where they do no harm : these are termed saj^hrophytes. Yet 

 others produce fermentations, such as tlie Vinegar- and Paste- 

 Eelworms. 



In all cases both egg and cyst of these Nematodes have the 

 power to resist extreme heat and cold, unless it be that the 

 former is kept up for some time. 



