Oligochaeta.] 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



285 



DiPOROCHAETA BBACHYSOMA. 



Natural size. 



with a greyish tint. The chaetae are inserted in pale spots. The pigment, appear- 

 ing brown in sections, is densely aggregated in the connective tissue of the circular 

 musculature, but there is also a little black pigment in streaks amongst the longi- 

 tudinal muscles. There is none in the epidermis. 



Dimensions. — The worm is remarkable for the breadth of 

 the short body. Its length is from 30 mm. to 35 mm. ; 

 diameter, 4 mm. The body contains 60 to 70 segments. 



Chaetae. — There are about 40-50 chaetae on each seg- 

 ment ; they are of the same size, but unequally spaced, those 

 near the dorsal surface being rather further apart than those 

 on the ventral region ; the spaces bear the proportion of 3 

 to 2 respectively. The ventral gap is greater than the dorsal, 

 as 5 to 4, the former being about three times larger than the 

 neighbouring interchaetal space, the latter four times the 

 nearest space. 



The clitellum covers segments 14-17, and completely encircles the body. 



Genital Pores, <&c. — The male pore is in a depression on each side of the 18th, 

 in line of chaeta b, which, as usual, is thrust outwards ; both chaetae a and b are 

 present, but are smaller than those of other segments. 



The spermathecai pores are at 7/8, 8/9. 



On the anterior margin of segments 18, 19, and 20 there is a pair of circular 

 admedian tubercula ptiberiatis ; there is, however, some variability, especially in 

 regard to the tubercula in the neighbourhood of the sperma- 

 thecal pores ; in one individual there is a pair at the an- 

 terior margin of the 8th, in another at the anterior margin of 

 the 9th, in others none are present in this region. 



The nephridiopores are, I think, in line with the 14th 

 chaeta — i.e., are high up on the body. 



The prostomium is half epilobic ; there is a transverse 

 groove, from which short longitudinal furrows pass back. 



Internal Anatomy. 



The septa behind segments 10-13 are thickened. 



The dorsal vessel, as it passes through 9-13, is narrow, 

 owing to the thick muscular wall ; in the 14th it loses most 

 of this muscular coat, and dilates to form the usual wide 

 vessel. The hearts are in the 10th, Uth, j.nd 12th, arising 

 not from a supra-enteric vessel, but directly from the enteric 

 blood-plexus, with which the dorsal vessel is connected in the 

 14th by four short vertical vessels. 



The pharynx is very powerfully developed, the retractor muscle and the glands 

 extending as far back as the 10th segment. I see no gizzard, even in sections. The 

 oesophagus in 10, 11, is narrow ; it dilates in 12, 13, and 14 successively, being con- 

 stricted by the septa through which it passes, and, as the wall is lamellate here, these 

 dilations may be regarded as glands ; it narrows again in 15, and widens into the 

 intestine in the 16th segment. 



The nephridia are small. 



DiPOROCHAETA BRACHYSOMA. 



Ventral view of genital 

 segments. 



(X 4.) 



