186 BULLETIN OF THE 



been shown to exist, and I have looked in vain for evidence of one in 

 Nectonema, The only indication of a dorsal line in Gordius is the 

 median dorsal interruption of the longitudinal muscles in the posterior 

 portion of the body ; in Nectonema, on the contrary, this organ is well 

 developed. In both forms the ventral line is prominent, and in both 

 it contains the ventral nerve cord. 



Of the nervous system it may be said that the brain is more highly 

 developed in Nectonema, the dorsal cells as well as the correlated an- 

 terior chamber being structures entirely without parallel in Gordius. 

 But the ventral nerve cord in the two genera shows a similarity not only 

 in position, but to a certain degree in structure, being made up in gen- 

 eral of three portions, a median and two lateral. (Of. Vejdovsky, '86, 

 Taf. XVI. Figs. 51, 63, et al.) Like many other Nematodes, both forms 

 possess an anal ganglion. 



Numerous lesser points of likeness may be mere coincidences. Such 

 are the great numerical superiority of males over females, — which, 

 among all Nematodes, is found only in these two groups, — the para- 

 sitic nature, and the mode of motion. The spermatozoa which I have 

 described recall the unripe sperm of Gordius ; yet such evidence is in- 

 teresting rather than weighty. 



In summing up this detailed consideration it may, I believe, fairly be 

 said, that the points of difference between Gordius and Nectonema are 

 more numerous than those of likeness, but that the latter are more 

 general and important. This agreement in general characters is so 

 striking that I cannot believe it is due to anything else than affinity. 

 It will be noticed that the characters which separate the Gordiidae from 

 the other Nematodes are shared with Nectonema ; thus the absence of 

 latei'al lines, the existence of one principal nerve cord (ventral), the dorsal 

 position of the sexual organs, and the terminal openings of the same. 

 Again, the points of difference between the two groups are largely 

 those which separate the various families of Nematodes s. str. from 

 one another ; namely, the structure of the muscles and alimentary ca- 

 nal (V), and the character of the ducts and external sexual organs. 



We do not know how much the change from salt to fresh water 

 has modified Gordius, which is evidently the more degenerate form, as 

 may be inferred, for example, from the greater reduction of the alimen- 

 tary canal and of the nervous system. Certainly the rows of bristles in 

 Nectonema are to be attributed to its free life and more active habits. 

 With the latter also one would naturally look for a more highly devel- 

 oped nervous system. Further evidence, that to be gained from the 



