PROPORTION OBSERVED IN THE SET^E OF CERTAIN NAIDID.E. 



785 



whole length of the seta, were: — (i) rather more than '5, '47, '41, '39; (ii) rather 

 more than '5, '46, '41. The series run from inner to outer side of the bundle. 



Dero limosa. 



Observations were made on the setae of posterior segments. Where these setae 

 are four per bundle, they can be distinguished as two couples, an inner and an outer ; 

 the outer couple is the shorter, and is especially short from nodulus to tip ; the 

 proportions, in a measured example, reckoned as above, being : — inner couple '44 and 



Text-fig. 1. — Arrangement of ventral setee in a 

 number of Naididse (diagrammatic). 



'41, outer couple both '30. In bundles of three there is a progression of the same 

 kind, the intermediate seta having intermediate proportions ; e.g. from inner to outer, 

 '45, '36, '33. 



Nais raviensis. 



This species, recently described by me (Records of the Indian Museum, vol. x, 

 part 6, 1914), shows the relations described above very typically. Taking the setae 

 of three segments, the actual lengths of the portions of the setae distal to the nodulus, 

 in order from the inner to the outer side, were found to be : — (i) 20, 17, 15, 12'5 m ; 

 (ii) 20, 19, 17, 15 m ; (iii) 20, 19, 17, 16 m. The proportions in these cases, worked 

 out relatively to the total lengths of the setae (which need not here be given), are : — 

 (i) '40, '39, '35, '30; (ii) '43, '41, '39, '36; (iii) '42, '41, '37, '36. 



Hsemonais laurentii. 



In the posterior part of the body, the distal segments of the setae become pro- 

 gressively shorter from inner to outer side of each bundle, thus agreeing with the 



