944 MR, H. K. MEHRA ON TWO NEW IJSTDIAN 



He places it as an appendix to the Tubificidae, thoitgh he thinks 

 that it fits neither with that family nor with the Lumbrieulidse, 

 and suspects that it may be necessary to found a new family for 

 it. Piguet (11) described a second species in 1906 and placed it 

 among the Naididae as jVaidmm pleuriseta ; but later transferred 

 it to Auloch'ihcs, which he considers to belong neither to the 

 Tubificidse nor to the Naididse, as he saw retractile penes in front 

 of the ventral setge of segment 7. He did not complete the study 

 of the worm, and so could not be sure about its position. 

 Stephenson in a paper (16) published in 1921 describes another 

 species, A. reinex, from India as above-mentioned. 



The genus, which hitherto has been characterized mainly by 

 the character of the needle setse (crotchets), is now well estab- 

 lished, as will be seen from the following description. The 

 genital organs^ unknown to all the previous authors, are described 

 at full length in the present paper and decide the position of the 

 genus in the family Tubificidae. The fact that the needle setse 

 possess a small outer prong (the one on the outer side of the 

 curve of the shaft), which is not the usual condition in the 

 Microdrili, is not of very great generic importance, because in 

 some TubiHcids, e. g. in Tubifex velutinus Grube, some crotchets of 

 a similar kind are present ; and moreover in A. stephensoni the 

 outer small prong is missing altogether, the needle setse being 

 thus singly pointed and not forked. 



The hinder end of the body is narrower and thinner, and does 

 not show any signs of segmentation. Sometimes a faint indica- 

 tion of external segmentation may be visible, but the zone of 

 budding lies some distance in front of the anus, where a large 

 number of new segments are being formed. One can easily 

 recognize the worm by its peculiar hinder end. This feature was 

 previously described by Piguet in A. pleuriseta, und Stephenson 

 has recently confirmed it in A. remex, and remarks "the most 

 posterior region shows no proliferation, nor even any segmenta- 

 tion, but there is a zone of proliferation and formation of 

 numerous new segments some little distance in front of the anus." 

 Later on, he adds " such a budding zone as that of the present 

 genus is so far as I know unique." 



Aidodrilus connects the genera Branchiura, KaioaTiiuria, 

 Fsammorcytes, and Tubifex ; it also shows some resemblance to 

 MonopylephorujS ajricanus Michaelsen in the points that it 

 possesses a spermiducal chamber, penial setae and spermathecae in 

 the 9th segment. In certain points it also bears some similarity 

 to the Naididae. One point of similarity, namely the anterior 

 position of the genital organs, is however merely a case of extreme 

 variation within the genus Aidodrilus and hence not of any 

 generic importance. This follows from the description here given 

 of a second species, undoiibtedly belonging to this genus, in which 

 the reproductive organs lie in the usual position for the Tubificidae, 

 That it is a Tubificid is beyond any doubt, but it shows a greater 

 simplicity of structure than any other genus of the family. 



