784 PROFESSOR J. STEPHENSON ON A PULE OF 



to what at that time appeared to be a peculiarity in a species of Aulophorus found 

 in Lahore (A. Stephensoni, Mchlsn.).* 



Here, in both an anterior and a posterior segment, the position of the nodulus 

 was found to vary regularly within the bundle, in such a way that while in the 

 innermost seta of a bundle the nodulus was slightly proximal to the middle of the 

 shaft, in the outermost seta it was markedly distal ; and the intermediate setae 

 showed intermediate conditions. The actual figures were : — 



(a) Segment iv. total length of setae 58, 58, 62, 54 ft, 



portion distal to nodulus 32, 29, 30, 12 ft. 



(b) A posterior segment, total length of setae 56, 56, 57, 53 ft, 



portion distal to nodulus 29, 26, 22, 18 ft. 



The series in each case begins from the innermost seta of the bundle. On 

 working out the ratio between the length of the distal segment and the whole length 

 of the seta, we find that in the anterior bundle the setae, in order from inner to outer, 

 have respectively "55, '50, "48, '39 of their length situated distal to the nodulus ; in 

 the posterior of the two bundles measured the proportions are '52, '46, '38, '34. In 

 other words, the position of the nodulus becomes regularly more and more distal on 

 the shaft from the inner to the outer side of each setal bundle. The condition is that 

 illustrated in text-fig. l.f 



Similar observations on other Naididae since the publication of the above have 

 shown that this condition is not confined to the species in which it was first notec 1 . 

 I give below the details for the species which I have examined. 



Aulophorus furcatus. 



In the anterior segments (ii-iv) the nodulus is proximal to the middle of the shaft 

 in the innermost seta of a bundle (distal to nodulus : proximal to nodulus : : 7 : 5) ; 

 in the middle setae it is at the middle of the length of the shaft ; and in the outer- 

 most it is either at the middle or very slightly distal. 



In the remaining segments (v onwards) the nodulus is usually distal to the middle 

 of the length of the shaft, but its position varies as in the example already given ; 

 i.e. it is more distally situated in the outer setae of a bundle than in the inner. 

 Thus in two cases the proportions of the distal segment (beyond the nodulus) to the 



* The worm was described as "a species of Dero found in Lahore" ; but since the species possessing palps are now 

 separated from those without, it becomes an Aulophorus. 



t The technical difficulties of observations on the seta; may be overcome by a method which is well explained by 

 Pigdet, "Observations sur les Naididees," Rev. Suisse de Zool., t. xiv, 1906. A living specimen is allowed to remain 

 in water under a cover-glass while the water gradually evaporates ; it becomes more and more compressed, and finally, 

 flattening altogether, disintegrates. A small drop of glycerin, placed ai the edge of the cover-slip at this stage, before 

 air is sucked in under the cover, will, as evaporation goes further, enter underneath the cover-slip and convert the 

 specimen into a permanent preparation. In successful preparations the setae, which can now be observed flat and in 

 one plane, are seen laid out in their proper order and disposition in the bundles, as shown in text-figs. 2 and 3 

 (taken actually from a preparation of Hcemonais laurentii) on p. 772 ant. 



