1 64 



NEMATHELMINTHES 



ch; 



especially with this question, such as Neumann's Parasites and 

 Parasitic Diseases of Domesticated Animals. A couple of cases will 

 show how important this matter is to the farmer. Crisp estimates 

 that Syngamus trachealis causes the death of half a million 

 pullets in England every year, and Megnin states that in a single 

 pheasantry 1200 victims died daily; again, the loss of one- 

 third the crop of beetroot is by no means uncommon when it 

 is infested with Heterodera schachtii. These show the practical 

 importance of what at first sight seem quite insignificant animals, 

 and the necessity for the minutest observation, for only when we 

 are fully acquainted with all the details of the life-history of a 

 parasite are we in a position to successfully combat it. 



Sub-Order II. Nematomorpha. 



Until the last few years it has been customary to regard the 

 Gordiidae as a family of Nematodes. Although in external 

 appearance and life-history they closely resemble the members ot 

 this group, yet recent research has shown so many important 

 morphological differences between them and the Nematoda, that 



most zoologists are now agreed in 

 placing them in a different sub- 

 Order, the Nematomorpha, a name 

 first suggested by Vejdovsky. 1 



The Gordiidae comprise but 

 two genera, Gordius and Necto- 

 nema. The latter has but one 

 species, JV. agile Verr., and is 

 marine ; the former, on the other 

 hand, is exclusively fresh -water, 

 and contains a very large number 

 of species. Gordian worms are 

 frequently to be found in ditches, 

 ponds, or large puddles, moving 

 with an undulating motion 

 through the water, or twining and 

 writhing round water-plants ; they are scarcer in running water. 

 In shape they are like a piece of thin whip-cord, slightly tapering 



1 F. Vejdovsky, Zeitschr. wiss. Zool. Bd. xliii. 1886, p. 369 ; Zeitschr. wiss. Zool. 

 Bd. xlix. 1888, p. 188. 2 Arch. mikr. Anat. Bd. xxxvii. 1891, p. 239. 



Fig. 82. A water plant around which 

 a female Gordius is twining and lay- 

 ing eggs, a, a, Clump and string of 

 eggs. (From von Linstow. 2 ) 



