DESCRIPTIONS OF GENERA AND SPECIES 267 



that, as Stolc has pointed out, Macintosh partially described this species in his 

 paper upon the structure of Tuhifex. He distinguishes ' two species ' of Tubifex, the 

 one which he considers to have most claims to be called Tubifex rivulorum, being 

 in all probability identical with Ilyodrilus coccineus j the reasons for this identification 

 are— (i) the shape of the setae ; Macintosh found no traces of the ' brush tip ' to 

 the uncinate setae of this form such as characterize the true T. rivulorum; as he 

 figures the latter kind of setae in the 'elongated form from the lakes' (really the 

 true T. rivulorum), it seems clear that no mistake has been made, even if it was 

 reasonable to doubt the accuracy of so experienced a worker ; (a) the integumental 

 network is particularly referred to as existing in the shorter form of 'Tubifex'; 

 (3) the peculiar brown glandular body lying upon the course of the nephridium is 

 figured (PI. ix. fig. 18) for the form which is to be regarded as the same as Stolc's 

 I. coccineus. Vejdovsky at first distinguished his T. coccineus from T. rivulorum; 

 in his work upon the Oligochaeta in general he places (p. 46) T. coccineus among the 

 synonyms of T. rivulorum, on the grounds that there are numerous transitions between 

 this form and the worm described by various authors as T. rivulorum ; as, however, 

 ' T. rivulorum ' of some authors is now fairly certainly known to be no less 

 than /. coccineus, this argument loses its force. Later (p. 146) in the same work 

 Vejdovsky, in dealing with the egg development, which is after the Naid plan, again 

 emphasizes the difierence between his T. coccineus and the common form, T. rivulorum : 

 there seems to be no doubt that Ratzel's description of the egg development in 

 ' T. rivulorum ' referred to the present species, and that there was no dimorphism 

 — as he thought —or pathological conditions — as thought Lankester and Nasse. Still 

 later, in a footnote to p. 156, VEJnovsKY refers to the worm as /. coccineus without 

 any explanation of his alteration of opinion, and in the section dealing with the 

 relationships of the Oligochaeta the same author mentions the sexual setae (mentioned 

 also in the place just referred to) as evidence of the relationships of 'Ilyodrilus' to 

 the Naidomorpha. It is difficult to understand how Vaillant, with Stolc's paper 

 upon Ilyodrilus before him, could have put it as a mere synonym of T. rivulorum ; 

 his reasons for doing this are because Vejdovsky thought so at one time, before the 

 species had been re-investigated by Stolc. It is the more remarkable that Vaillant 

 should have overlooked the differences between the two species, as Ilyodrilus is so 

 thoroughly intermediate between the Naids and the Tubificids, which Vaillant unites 

 into one single family. To have emphasized its differences from Tubifex and resem- 

 blances to Naids would have greatly strengthened Vaillant's position 



I take this opportunity of referring to Nicholson's Saenuris canadensis (see Vereill) merely 

 for completeness' sake, as it is unidentifiable. 



M m 2 



