NEMATODE WORMS. 



67 



circle of spines. Tliey moult their skin . frequent ecdyses or 

 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 {Oxyiiris). In 

 the Ascaridce 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 



Fig. 21. — ANauiLLULiD.E (Eelworms). 



, Mature 9 with oral spine ; h aBd c, ova ; d, extremity of c5 ; 

 (Enlarged, after Ritsema Bos.) 



e, anterior oT adult. 



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

 life during some period of their existence. Those that are 

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

 cockles 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 saphrophytes. Yet 

 others produce fermentations, such as the 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. 



