1903. J OLiaOCH.ETA FROM NEW ZEALAND. 211 



moderately extensive. The sperm-duct is comparatively thick ; it 

 passes below the ovary nearly directly backwards to the hinder 

 septum of the twelfth segment ; there it makes a single loop round 

 the neck of the atrium, and then runs up it to enter its distal 

 extremity. 



This atrium (or spermiducal gland — for it is both) is a large 

 pyriform or sausage-shaped sac, with a capacious cavity ; its 

 broader end is directed upwards, its naxTOwer end is suddenly 

 constricted to form an extremely short and narrow duct, just long 

 enough to pass through the body- wall. In its microscopic structure 

 the atrium presents what is probably to be regarded as an archaic 

 character ; at any rate, it is simpler than that of any Tubificid 

 hitherto described. The epithelium consists of a single layer of 

 tall, glandular, and much vacuolated cells, outside which is a thin 

 peritoneal membrane with flat nuclei (PI. XXIV. fig. 9). There is 

 apparently no muscular coat, except for a few circular fibres near 

 its lower end where it is about to penetrate the body- wall. 



In the figure (fig. 9, which is drawn under a camera, and 

 represents as accurately as may be the arrangement of the 

 nuclei and vacuolation of the cytoplasm) two kinds of nuclei are 

 to be seen in the epithelium : most of them are circular and 

 situated towards the outer surface of this epithelium ; others, 

 however, are oval, elongated in a direction vertical to the surface, 

 these lie nearer the inner ends of the cells. These latter suggest 

 a columnar epithelium distinct from the gland-cells ; but I have 

 been unable to detect any cell boundaries corresponding to these 

 oval nuclei, which, moreover, are not arranged in close array to 

 sviggest an epithelium. It may very well be, however, that some 

 of the epithelial cells are short and have not become glandular. 



The sperm-duct opens into this atrium at its apex, i. e. at the 

 point furthest from the external opening. In this feature it bears 

 a nearer resemblance to Branchiura coccinea than to B. sowerhyi ; 

 but even in the former species the duct enters the side, rather 

 than the apex, of the nearly spherical atrium. 



The copulatory chcetce form a bundle (varying from only 3 to 

 as many as 7 or 8) of simple bristles, lying in a pit or depression 

 near the male pore. Viewed from the side in a mounted speci- 

 men, the two organs appear coincident ; but sections show the 

 true relation. Each of these chtetae, one of which is figured 

 (PI. XXIV. fig. 7), is a nearly straight rod, thicker than the 

 other chsetae, terminating in a point, which is not terminal, but 

 directed to one side. 



The spermaUieca is globular, with a well-marked duct about 

 half as long as the diameter of the ampulla. The neck of the 

 latter is provided with a ring of elongated glandular cells, forming 

 a prominent, valve-like structure (in longitudinal section). The 

 duct is lined by cubical gland-cells, and is provided with a 

 muscular coat. There are no spermatophores. 



Dimensions. Length of an entire individual 15 mm.; diameter 

 I mm. Number of segments 70. 



14* 



