186 ON A COLLECTION OF EARTHWORMS FROM NEW BRITAIN, THE 



that we have to do with the same species. I cannot, after carefully comparing the 

 new specimen with those from Upolu (one entire specimen I fortunately possess), see 

 the slightest reason for separating them, although as will be seen I am able to add 

 some details to my original account of this Perichaeta. Perichaeta upoluensis is a 

 species which varies considerably in size. The largest of the examples collected by 

 Dr Willey measures 166 mm. in length and consists of about 110 segments. The 

 smallest example, but equally mature as regards the development of its sexual organs, 

 is only 92 mm. in length and consists of but 95 segments. 



This worm is characterised by a purplish tinge upon the dorsal surface. The 

 dorsal pores commence between segments X and XI. 



As I have already mentioned, the most characteristic feature of this species is the 

 number aud arrangement of the copulatory papillae. These show some variation from 

 specimen to specimen, with of course the same general disposition. The papillae are 

 in every case very small contrasting with those, for example, of Perichaeta sedgwickii 

 just described. 



Their characteristic feature ( Fig. 1 ) is that a number of segments immediately 

 following the clitellum have a single median papilla. They are not paired. I shall 

 now describe the arrangement of the papillae in detail in the four specimens ; this is 

 by no means a waste of time or space, since species of Perichaeta are occasionally 

 mainly or even entirely to be discriminated by the number and the arrangement of 

 their papillae. And since furthermore some species have been described as to these 

 organs from a single example. It is highly important therefore to take note of the 

 variations which these structures exhibit. From a detailed account of the variations 

 a general notion of the characteristics of the species can be obtained. 



In one specimen there is a single papilla on each of segments X, XVII — XXI; 

 and in addition to these median papillae two near to each male pore. One of these 

 lies to the inside and above the pore, the other to the outside. In a second specimen 

 there is no papilla upon segment X. But the median papillae in the neighbourhood 

 of the male pores are increased by an additional one upon segment XXII. Moreover 

 that upon segment XXI was double. The two papillae close to the male pores are 

 increased in this individual to three. 



In specimen No. 3 I did not detect a papilla upon segment X. But there 

 were six on the segments following the clitellum, i.e. on XVII to XXII. A triangle 

 of a papillae surrounded each male pore. 



In the largest individual of this species there are only five papillae of the median 

 series, thus showing that it is not always possible to assume that the largest individuals 

 are more completely mature than smaller specimens. There was no papillae on X 

 and only two in the immediate neighbourhood of the male pores. In my original 

 account of this species I described a median papilla upon segment IX not upon 

 segment X, as in one of the individuals collected by Dr Willey. It occurred to me 

 that I might easily have made a mistake, aud fortunately I have by me one of the 

 specimens from which that description was compiled. I find on re-examination that 

 I did not fall into an error in this matter. 



The clitellum fully occupies segments XIV — XVI. I could not find any setae 

 upon it. 



