WOKMS. 219 



shaped lips. In the male the hinder end of the body- 

 is usually bent in a hook-like manner. The anus is 

 not placed quite at the hind end of the body. All 

 the species inhabit the alimentary canal (Cf. p. 211). 



Horse Worm {Ascaris megalocephala). Male six to 

 eight, female twelve to seventeen inches long ; some 

 times occurs in great balls, causing stoppage. 



Round Worm of Cat (Ascaris mystax). Male two to 

 two and two-fifths, female four and four-fifths to five 

 and one-fifth inches long; in the intestines of the 

 cat. Ascaris ffiarginouta infests the dog. 



Pinworm (Oxyuris curvula). Male one-fourth to 

 one-third, female one and four-fifths of an inch long. 

 In the rectum of the horse, causing persistent itching. 



Family : AnguillulidsB (Edworms). 



Extremely small, thin-skinned; lay only a few 

 relatively large eggs, which develop very quickly. 

 With few exceptions either earth eelworms (i.e. live 

 in decomposing organic matter or humus soil) or as 

 plant parasites leading to characteristic diseases of 

 wild and cultivated forms. All these parasitic forms 

 have a " mouth spine." This structure, found in the 

 mouth cavity, is very sharp and pointed in front, and 

 can be worked forwards and backwards so as to 

 penetrate the cell walls of plants. A mouth spine is 

 not only found in the species which infest plant tissues 

 (several species of Tylenchus and Aphelenchus, as well 

 as all the known species of Heterodera) , but also in 

 those forms living free in the earth which bore into 

 the exterior of plant roots (the remaining species of 

 Tylenchus and Aphelenchus, Borylai/mus, etc.). In 

 all cases an eelworm, devoid of a spine, is not a plant 

 parasite. I will only deal with those parasites by 

 which well-known destructive diseases of cultivated 

 plants are caused. These belong to the genera Ty- 

 lenchus and Heterodera. The first remain eel-shapeA 



