184 ON A COLLECTION OF EARTHWORMS FROM NEW BRITAIN, THE 



has mentioned in this species a single caecum placed rather further forward. This 

 is, as I believe, an absolutely unique character in this genus. I was therefore 

 particularly careful to endeavour to confirm or to deny Benham's statements. I may 

 say that I found this single unpaired caecum in three specimens which I thought 

 sufficient to dissect for the purpose; there can therefore I think be no doubt that 

 we have here a genuine specific character and not a mere abnormality as might be 

 suggested. The single caecum is in its characters precisely like one of the two 

 caeca where there are two. It has the same somewhat crinkled aspect that the caeca 

 of Perichaeta possess ; and it is not unusually large so as to suggest a fusion between 

 a medianly approximated pair. 



One fact in the structure of this species has been apparently overlooked by 

 Benham. He does not refer to the existence of genital papillae except a pair on either 

 side of the male pores. These papillae (Fig. 3) are by no means always distinct; but in 

 one of the individuals which I studied were quite obvious although forming somewhat 

 faint impressions upon the body-wall. Those papillae, though faintly outlined, are 

 very large and occupy nearly the whole of the available space on the ventral side 

 of the body. They occur both in the neighbourhood of the male pores and of the 

 spermathecae. On each of segments XVII, XIX, XX, XXI, are a pair closely approxi- 

 mated to each other on the ventral surface of those segments, in front of the line 

 of setae. In addition to these the XVIth to the XXth segments possess a pair of 

 papillae situated to the outside of the set that has just been described. These latter 

 are in fact on a line with the male pores. These papillae lie partly behind and partly 

 in front of the setae of their respective segments, overlapping them in front. Those 

 of the XVIIth ' and XVIIIth segments are more intersegmental in position, extending 

 in each case a little way on to the following segment ; they remind one much of 

 the articular surfaces for ribs on two adjacent vertebral centra. It is these papillae 

 only that Benham has referred to in his account of Perichaeta sedgwickii. The papillae 

 in the neighbourhood of the spermathecal pores are placed on segments X — XIII. 

 On each of these segments are a pair of ventrally placed papillae lying in front of 

 the row of setae. 



The other characters of the worms that I refer to Perichaeta sedgwickii agree 

 so absolutely with the description given by Benham that I cannot doubt that they 

 are specifically identical. Here however is a character, not always obvious, that when 

 missing or apparently missing might have easily led to the creation of a new species, 

 if but one example had been under observation. 



Perichaeta Malamaniensis, Benham. 



P. malamaniensis, Benham, loc. cit., p. 213. 



Dr Benham's two species Perichaeta arturi and P. malamaniensis evidently come 

 very close together. They agree to differ from all species of which at any rate we 

 have adequate knowledge by the existence of a complex copulatory apparatus, which 



1 The outer papillae of segment XVII are not visible in the specimen figured. 



