18y0.] WORMS OF THE GENUS PERICH.«TA. 57 



(5) Genus Hoploch.eta, gen. nov. 



Setse forming a continuous row round each segment ; atria tubular, 

 two pairs opening on to segments 1/ and 19. 

 (For P. stuarfl. Bourne.) 

 Distribution. India. 



Perich^ta indica (Horst). 



'Eine Perichceta von Java,' Horst, Nederl. Arch. f. Zool. iv. p. 3. 



Megascolex indicus, Horst, Notes Leyden Mus. vol. v. p. 186. 



PerichcBta 2«6?/ca, Beddard, Proc. Zool. Soc. 1886, p. 298; Horst, 

 Midden-Sumatra, Vermes, p. 4. 



This species is already pretty well known, and I have not much 

 to add to our knowledge of it beyond the appearance of the living 

 worm, which has been already described (p. 52) and which is 

 illustrated in the accompanying coloured drawing (Plate IV. fig. 1). 

 Horst remarks (15. p. 189) that probably some of the specimens of 

 P. cingulata described by Vaillant (22) are identical with this 

 species ; Perrier has suggested that several species are included under 

 the name of P. cingulata. In view of these difficulties it seems to be 

 reasonable to adopt Horst's name of P. indica and to drop the name 

 of P. cingulata altogether. 



On the first few segments of the body there are two specially 

 large and distinct pairs of setee, situated at almost equidistant 

 intervals on the ventral side of the body. I did not refer to them 

 in my earlier paper upon P. indica ; the condition of the setae is a 

 step in the direction of those very remarkable Perichfetous worms 

 described by Mr. Fletcher, which I have ventured to include in a 

 distinct genus. These facts have an important bearing upon the 

 general question of 



The Distribution of the Seta in Chcetopods. 



The paired setae of Lumbricus and other Oligochseta are usually 

 compared to the parapodia of the marine Chsetopods ; and it has 

 been supposed that four distinct parapodia and four pairs of setae 

 represent the typical arrangement of the locomotor organs of these 

 two divisions of the Chsetopoda. Deviations from this arrangement, 

 the extremes of which are shown in the Capitellidse and in the 

 genera Perichceta and Perionyx, are regarded by perhaps the ma- 

 jority of naturalists as secondary modifications. There is, however, 

 a certain amount of evidence which seems to point the other way, 

 indicating that the complete circle of setae, which characterizes the 

 family Perichaetidae, is the primitive arrangement; in this case the 

 paired setae of Lumbricus, Acanthodrilus, &c., will be due to 

 reduction, and the comparison with the four seta-bundles of Poly- 

 chseta will fail to the ground. x\mong Polycbaeta the nearest 

 approach to the Perichaetous coridition is found in the Capitellidse ; but 

 Eisig (13) argues with considerable force against regarding the almost 

 continuous circle of setae found in some Capilellids as the primitive 



