202 Memoirs of the Indian Museum. [Voiv- I, 



Note. — Since writing the above account I have been able to obtain a fair number of sexual 

 individuals, with the organs in various stages of development. Unfortunately I am unable to work 

 through this material at present, but hope to have an opportunity of returning to this subject. 



Parasite. — In almost all cases there are a number of protozoan ectoparasites 

 attached to the head, and in smaller numbers to other parts of the body, of these 

 worms. Strictly speaking they are commensals rather than parasites, since occa- 

 sionally they are found attached to the setse, and hence cannot then draw any 

 nutriment from the body of the worm. I have not identified the form, though 

 it appears to be related to Spirochona. It is of a vase shape, with stiff processes 

 projecting from the rounded angles of its free extremity ; these are actively motile, 

 performing sharp sudden movements inwards at irregular intervals ; there is also a 

 spirally coiled ciliated oral process. The animal is attached by a ''foot"; the 

 nucleus, as brought out by acetic acid, is moniliform, with a . narrower central 

 portion, or may appear as divided into two separate halves (plate xx, fig. 49 a-e). 



The species described above has a certain similarity to N. elinguis, O. F. M., 

 and agrees in most particulars with the diagnosis given by Michaelsen [3] in 1900 ; 

 and I was at first inclined to consider this form as, at most, a variety of N. elinguis. 



Through the kindness of Dr. Piguet, I have recently received a copy of his 

 dissertation [7] on the Naid'dse of Switzerland. He remarks as follows: "La 

 systématique des Nais était très incomplète, les diagnoses souvent insuffisantes. La 

 description sommaire de N. eling^ns s'applique à au moins 3 Nais différentes, et le 

 désaccord entre les zoologistes au sujet des espèces de ce genre s'explique très facile- 

 ment. Une détermination exacte basée sur une description rapide des soies est 

 impossible, et permettrait de confondre A^. communis, N. variabilis et N. elinguis, 

 qui ont toutes trois des aiguilles bidentées et des soies capi laires dans les faisceaux 

 dorsaux; et cependant ces trois espèces sont parfaitement distinctes." 



Of the species and varieties into which the old N. elinguis has thus been broken 

 up, the one which most closely resembles the present form is N. variabilis. From 

 N. elinguis as now defined the present form is distinguished by the constitution of the 

 dorsal bundles, which in N. elinguis have a larger number of component setse ; and by 

 having shorter terminal prongs to the dorsal needle-setse ; the distinction between the 

 ventral setse of segments ii-v, and those which follow them is also wanting in 

 N. elinguis. From N. communis, Piguet, also it is distinguished by the colour, the 

 less marked bifurcation and less obvious nodulus of the dorsal needles, the frequent 

 bifid termination of the genital setse, and apparently by the very definite difference 

 in the thickness of the ventral setse in segments ii-v and of those posterior to 

 this. 



In considering N. variabilis, Piguet, we have to take into account the type form, 

 the variety of the large lakes of Switzerland, the variety with very long hair-setse, 

 N. variabilis, var. simplex, and a form called by Piguet ''seconde forme annexe." I 

 have gone carefully through these forms, which differ among themselves in details 

 of colour and relative size and visibility of the prongs of the dorsal needle-setse. 



