56 



OHAPTEE V. 



WORMS (vermes) — Continued. 

 Xemathelminthes or Eodnd-Woems. 



The Eound - worms have a tubular and filiform body. The 

 cuticle, or outer layer of skin, is ringed but never segmented. 

 The sexes are separate, the male worm being usually quite dis- 

 tinct from the female. The alimentary canal may be absent 

 or rudimentary, but is generally present and well developed. 

 There are no special organs of respiration or circulation. 

 Amongst these round-worms innumerable parasitic forms are 

 found in man and the domestic animals, as well as in fish and 

 insects. Many fatal diseases are produced by them, such as 

 trichinosis in man and pigs, gapes in poultry, husk or hoose in 

 lambs, &c. The horse is very subject to a number of species. 

 These worms taper to a point at each extremity.^ We shall 

 frequently observe special organs for attachment on both the 

 anterior and posterior regions, such as hooks, teeth, and even 

 suckers, which are used by the worms not only for holding on 

 to their host, but also for purposes of copulation. The integu- 

 ment of these round-worms has a thick cuticular layer, and also 

 a large muscular layer within, by means of which the body is 

 enabled to wriggle, undulate, and knot itself into fantastic 

 forms. Although vascular and respu-atory systems are seemingly 

 wanting, yet a nervous system exists. Here also we shall oh- 



' Except in the Strongylida:, wliere the posterior end of the male cul- 

 minates in a cup-shaped bursa. 



