NEMATOMORPHA LIFE-HISTORY 



173 



as Zeuciscus phoxinus, the minnow, Colitis barbatula, the loach, 



and Petromyzon planeri, the lamprey ; in the larvae of Diptera, 



Ephemera, and beetles, in Planorbis (a 



water snail), in Enchytraeus (an Oligo- 



chaet) ; the second larval form in all 



kinds of insects, spiders, Crustacea, 



fish, frogs, birds (Otis), and in man, 



and these various habitats lead him 



to the conclusion that " Les Gordiens 



n'ont pas d'hotes speciaux." On the 



other hand, as von Linstow points out, 



it is contrary to our knowledge of 



parasites that a single species should 



develop equally well in the body of 



warm and cold-blooded Vertebrates and 



of Insects, and the explanation of the 



presence of the larvae in these various Fig. 91. Tarsal joint of an 



1 .tit Ephemend larva into which 



forms may either be that they be- 



may 



two Gordius larvae (a, a) have 

 penetrated. Magnified. (From 

 G. Meissner.) 



long to different species of Gordius or, 

 more probably, that they are acci- 

 dentally present, having passed into their hosts with drinking 

 water. 



The number of species of Gordius is large ; over 100 are 

 enumerated in the Compendium der Helminthologie} the great 

 majority of which inhabit insects. 



The life-history of Nectonema is practically unknown ; the 

 adults have been found swimming near the surface of the sea at 

 two places only : Newport, E.I., and Wood's Holl, Mass., on the 

 south coast of New England. It has been fished close to the 

 shore, from the end of June to the beginning of October, when 

 the tide is going out at evening and there is no moon. This 

 seems to indicate that it avoids the light. When first caught 

 the worms move actively about, coiling themselves into figures of 

 eight and then uncoiling ; at the same time there is a rhythmical 

 movement caused by waves of muscular contraction passing down 

 each side of the body alternately ; by this kind of motion they 

 make rapid and definite progress through the water. 



It seems probable that the adult Nectonema is preceded by one 

 or more larval stages, and what appears to be a young form has 



1 Von Linstow, Hannover, 1878, and Nachtrag, 1889. 



