MUSEUM OF COMPARATIVE ZOOLOGY. 185 



strong resemblance to the second type. At any rate, I am unable to 

 see the striking difference in this region on which Biirger lays great 

 stress. As for the intestine proper, it is not of great importance whether 

 the lumen be bounded by four or eight cells. There are evidently dif- 

 ferences in the alimentary canal of the two forms; one of the most 

 striking is the degeneration of the anterior portion in Gordius, and of 

 the posterior part in Nectonema. This is, however, of minor impor- 

 tance on the question of general relationship. 



At first sight nothing could appear more unlike than the reproductive 

 systems in the two forms, and so far as external sexual organs are concerned 

 there does exist a great difference. The papilla and terminal opening 

 of the male Nectonema do not resemble in the least the forked tail and 

 subterminal opening of Gordius. The female organs bear an external 

 resemblance, but internally there is nothing in Nectonema parallel to 

 the complicated structure of the system in Gordius. Too little is known 

 of ovaries or testes in Nectonema to permit of a comparison, but the 

 apparent absence of mesenteries and the probability that the organs 

 are not paired in this case are certainly important differences. On 

 the other hand, certain striking points of similarity must be noticed. 

 The position of the sexual organs dorsal to the intestine is a peculiarity 

 in Nectonoma wliich is shared only by Gordius among all the Nema- 

 todes at least. The same may be said of the fact that both male and 

 female sexual organs possess terminal or subterminal openings. If 

 my conjecture be correct that in Nectonema this is a cloa'cal opening, 

 then this feature is also common to both. Moreover, of all Nematodes 

 these two families are the only ones in which spicula are entirely 

 wanting. 



The body cavity in the two forms differs in that a lining epithelium is 

 present in Gordius, but probably absent in Nectonema, except in the 

 anterior chamber. The body cavity of both increases in size, however, 

 by the cell masses which bound it taking part in the formation of sexual 

 products or the nourishment of the body ; but it is doubtful if this 

 process goes so far in Nectonema as in Gordius, where it leaves only a 

 thin row of cells, the peritoneal epithelium. This matter is, however, 

 hardly cleared up for Gordius, even after the numerous investigations 

 that have been made, and it cannot be regarded as more than formu- 

 lated for Nectonema by the present study. 



The lateral lines, as well as the contained excretory canals which are 

 so characteristic of all other Nematodes, are wanting in both Nectonema 

 and Gordius. In Gordius, moreover, no probable excretory system has 



