Olii/dchac/a.] 



•SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



279 



Dimensions. — The iiuiture worms vary from lUO mm. to 125 mm., with a 

 diameter of 4 mm. or 5 mm. There are from 126 to 130 segments. 



The chaetae are, of course, 8 per segment. The ventral chaetae are close to- 

 gether ; the dorsals are further apart, the distance being about equal to the lateral 

 space between the two couples. The ventral gap is greater than the lateral, and the 

 dorsal still greater, equal to about | of the circumference of the Ixidy. The formula, 

 then, reads : ah = \cd ; be = cd ; aa = 4 ab ; dd = 8 ah 

 = 2^ be. The line d is straight — i.e., there is no shifting 

 of the dorsal chaetae, as in certain other species. 



The elifeUum is saddle-shaped on segments 13-18 (six). 



Genital Pores, (&c. — On segment 18 is a pair of small 

 papillae, in line with the ventral chaetae, from the outer 

 margin of which a slight longitudinal ridge crosses the seg- 

 ment. The actual male pore is c^uite minute, in line with h. 



Tuhercula puhertatis are present in all the mature and 

 even in some of the immature worms — i.e., those in which 

 the clitellum is not present (? past the breeding season). 

 There are four pairs of intersegmental tubercles in line 

 with ab, at 15/16, 16/17, 19/20, and 20/21. There is also 

 usually a pair at 10/11, and sometimes at 11/12; either 

 of these may be absent. These tubercula have the form of 

 oval depressions, with a raised margin, and a small papilla 

 rising from the centre, which appears to be pitted. 



The spermathecal pores, though not recognisable on the 

 exterior, lie at 7/8, 8/9, in line of a. 



Nephridiopores are in line b, also unrecognisable from 

 the exterior. 



The prostomium is one-third epilobic, and has ^no transverse groove. The 

 preclitellar segments are bi- or tri-annulate ; the posterior ones are biannulate. 



Internal Anatomy. 



There are thick septa behind the segments 9-12, while those behind 13 and 14 

 are somewhat less thick. The last heart is in the 12th segment. 



The gizzard is in the 6th, and there is a relatively long piece of oesophagus in 

 front of it, a " proventriculus," which is dilated and thrusts the anterior end of the 

 gizzard back to the level of 7/8, while its posterior end is at the level of 9/10, so 

 that its length equals that of two segments. The oesophagus is narrow in 8, 9, and 

 10, having the usual lamellate wall ; in segments 11, 12, it is somewhat dilated, and 

 constricted by the septa ; in 13. 14, these lamellae are higher : and in the 15th the tube 

 is enlarged to form a swollen globular " oesophageal gland," though I do not detect 

 any calcareous particles therein. In the 16th and 17th it again narrows, and then 

 opens into the intestine in the 18th segment. 



The nephridia are small, and without a bladder ; the greater part lies at tJie 

 level ab. There is a pair of compact " peptonephridia," one on each side of the 

 pharynx, at its hinder part. 



Testes and ovaries are normal. Two pairs of sperm-sacs lie in 9 and 12, the 

 former small, the latter large ; both are lobulated. (In one specimen an additional 

 sperm-sac lies in the 14th.) 



Plutellus adcklamucus. 



Ventral view of the genital 

 segments, somewhat diagram- 

 matic. (X 5.) 



