18 ILLINOIS BIOLOGICAL MONOGRAPHS [138 



branching, but I have been unable to find any branching forms and, from 

 the manner in which they develop, I do not believe that branching forms 

 occur in this species. The branching forms probably occur on some other 

 species that Montgomery regarded as identical with this. The bristles are 

 more abundant at the two ends. In the males on the outside of the prongs 

 they are slightly longer than elsewhere and usually curved, while on the 

 inner surfaces there are very short, conical setae (Figs. 121, 122, 123). No 

 special bristles are located around the anus of the male (Figs. 96, 97, 98). 



Eggs and larvae. In nature the eggs are laid in thick cords which break 

 up into pieces seldom more than 10 to 15 mm. long and of a diameter 

 nearly equal to that of the worm. The larva belongs to the type with a 

 single terminal spine at the posterior end. In the newly hatched larva 

 (Fig. 20) the body is about twice as long as the proboscis but later becomes 

 much reduced (Fig. 14). 



Montgomery at first referred this species to Gordius aquaticus var. 

 robustus. Later he regarded it as Gordius villoti and eliminated the variety. 

 It belongs to the group known by most European writers as Gordius aquati- 

 cus. The identification is usually based on ViUot's description of what he 

 regarded to be Dujardin's Gordius aquaticus. Rosa regarded the identity 

 of the two species as impossible or at least highly improbable and called Vil- 

 lot's species Gordius villoti. At the same time he redescribed the species, 

 basing his description on a male and two females. He found on the surface 

 irregularly polygonal areolae which it is difficult to interpret as the rhom- 

 boidal areas in the cuticula. Villot later called them pseudoareolae and he 

 as well as Camerano included them in the description of Gordius aquati- 

 cus, stating that they are not present in all specimens. Of Rosa's specimens 

 only the male possessed the dorsal and ventral bands and the character is 

 not included in the original description of Villot's species. It is however 

 mentioned in the description of Dujardin and ViUot's later descriptions. 

 I have never found the bands absent on any specimen of Gordius robustus 

 or Faragordius varius and believe the character is not variable within a 

 species. On account of this and other differences between the male and 

 females described by Rosa it seems certain that he included at least two 

 species in his description, and it is possible that neither of them was identi- 

 cal with Villot's species. 



Rosa believes that Villot's species can not be identical with that of 

 Dujardin because Dujardin's description mentions pores 0.006mm. in 

 diameter in the fibrous cuticula which Villot does not mention. On the 

 other hand Villot mentions a dark collar behind the white anterior end, a 

 postcloacal crescent in the male and clear spots in the cuticula not mention- 

 ed by Dujardin. Villot in 1886, however, does describe pores in the fibrous 

 cuticula which he claims may attain the diameter of 0.006mm. On the 

 other hand Dujardin describes clear areas 0.06mm. in diameter which he 



