174 Traiisactiuns. 



The work \va« suggested to me by Professor Benham,* to whom. I here 

 record my thanks for his advice and suggestions during the course of the 

 investigation, as well as for the literature which he so kindly put at my 

 disposal out of his own library ; and had it not been for his assistance in 

 preparing the paper for publication I do not suppose it would have seen 

 the light. 



Nephridiopores. 



The i^ores present that alternation in their position in relation to the two 

 couples of chaetae which is a feature of so many genera from the South 

 Island. The alternation of the nephridiopores was originally discovered 

 by Perrier in PJutellus; then Beddard noted, in 1885, the same fact in 

 certain S2:)ecies of New Zealand earthworms — Maoridrilus uliginosus 

 Hutton {Acanthodrilus novae-zealandiae Bedd.) and 31. dissimilis. Later 

 Benham (11) added Plagiochaeta to this category, and gave tables illustrating 

 the irregularity of this arrangement in Neodrihis and Plagiochaeta. Although 

 this was at one time regarded as a peculiarity of our native worms, yet it 

 does not occur in all the genera, nor is it confined to those of this country. 

 It even occurs in some of the European species, in which it was for a long 

 time Supposed (and even in text-books is still stated as a fact) that the 

 pores were invariably in line wdth one or other of the couples of chaetae, 

 according to the genus. But Borelli, as long ago as 1887, described (13) 

 this irregularity in position in species of Lumhricus and Allolobophora ; and 

 in 1892 Hubrecht added further instances (21) amongst European worms. 

 But in these it may rather be described as an " irregularity " than as a 

 regular " alternation " in position. 



The nephridiopores of M. rosae lie either in front of the dorsal or in 

 front of the ventral chaetae, showing a broken alternation between the two 

 positions. 



The dorsal nephridiopore is in front of chaeta 3, or in front of the 

 gap between chaetae 3 and 4 (which form a closely apposed couple) ; the 

 ^'entral is in front of chaeta 2. 



There is no third position such as is described by Hubrecht between the 

 dorsal (upper) pair- of chaetae and the median dorsal pore, for the two pores 

 are seen to be superior or inferior in every segment, except, of course, the 

 first and the last, in which there are no nephridia. The pores of the first 

 pair of nephridia, however, are placed at the extreme anterior end of 

 segment 2, in line with the prostomial furrow. 



Beddard, in his " Monograph of the Order Oligochaeta," says that the 

 nephridiopores of Acanthodrilus (Maoridrilus) rosae are regularly alternate ; 

 but this is not so. They show, however, not a complete irregularity, but 

 rather an interrupted regularity, similar to that of Plagiochaeta punctata 

 as described by Benham. In some parts of the worm (though never at the 

 extreme anterior end) there occurs a regular alternation between the dorsal 

 and ventral positions for about twenty segments, and in examining such 

 a part one is led to infer that all the pores are similarly arranged. But in 

 the succeeding segments a break in the regularity occurs, and in this region 

 there are generally more pores in the dorsal than in the ventral position. 

 These segments past, the regular alternation is resumed, and is carried on, 

 with similar interruptions, to the posterior end of the worm. 



* This paper formed the basis of a thesis for honours in zoology at the University 

 of New Zealand in 1911 ; but since then it has received additions, has been subject 

 fco much rearrangement, and has suffered a great deal of contraction. 



