234 



ZOOLOGY 



Habits and 

 abundance 

 of thread- 

 worms 



Parasitic 

 thread- 

 worms 



monly in water or damp earth. They are not ciliate. 

 The sexes are almost invariably separate. They are 

 divided into the Nematoda 

 or nematodes ; the Nemato- 

 morpha, which include the 

 hairlike Gordius ; and the 

 Acanthocephala, a group of 

 curious parasites having re- 

 curved hooks on the proboscis. 



The nematodes, or typical 

 threadworms, exist in the 

 greatest variety and abun- 

 dance. They are parasitic on 

 animals and plants, many 

 of them infesting man. 

 Although the parasitic forms 

 are best known, Dr. M. A. 

 Cobb, who has paid special 

 attention to the subject, be- 

 lieves that the free-living 

 ones, when fully described, 

 will prove even more numer- 

 ous. He states that the 

 nematodes in a lo-acre field, 

 if arranged in single file, 

 would form a procession long 

 enough to reach around the 

 world. 



To give some idea of the 

 numbers occurring as para- 

 sites, we may cite the case of a young horse in which 

 were found 500 Ascaris, 190 Oxyuris, several millions 

 of Strongylus, 214 Scleroslomum, and 287 Filaria, not 

 to mention a quantity of tapeworms. Some of the 



B 



From Nicholson's "Classifica- 

 tion of the Animal Kingdom" 



FIG. 58. A ncmatode worm (Rhab- 

 ditis bioculata), female, enlarged. 

 g, gullet ; v, muscular gizzard ; s, 

 stomach ; i, intestine ; o, ovary ; 

 p, genital pore. 



