22 



AKIHA IIZUKA. 



A. Characters of the adult animal. 



In the living state, the annelid in question is of a white color with a 

 light pinkish tint ; a single dorsal hlood vessel is seen through the more 

 or less transparent wall of the body, as a bright red line running antero- 

 posteriorly and giving off lateral branches. 



The body (fig. 1) is long and slender, measuring 90-1 10 mm. in 

 length, by 3-3.5 mm. in breadth. The number of segments varies from 

 100 to 105 according to individuals. The breadth of the body increases 

 from the first to about the sixth segment, and then remain nearly the 

 same until the seventeenth. The eighteenth segment has a pair of pad- 

 like longitudinal ridges, on which account it is wider than any other 

 segment. From the next succeeding segment (19th) the body tapers 

 gradually towards the last, or anal, segment. 



The prœstomium (fig. 2, pr.) is present, but small, being separated 

 from the first segment or the peristomium (fig. 2, per.) by two curved 

 grooves, which converge posteriorly. 



The clitellum (fig. 2, cl.) is well developed all around the body, 

 occupying segments XII-XVII. 



A pair of pad-like longitudinal ridges (figs. 1 & 3, p.) is developed 

 on the ventral side of the eighteenth segment. They hang out on 

 each side somewhat like the pads of a saddle. Its free edge is bent 

 inwards, i.e. mediad, so as to overhang the male pores which open on 

 that segment. The genital papilla (figs. 1 & 3, g.p.) occupies the 

 ventral median portion of segments XIX and XX, both of which con- 

 tribute to its formation. It is elliptical in outline, with the major axis 

 disposed transversely and has a central depression. 



The setre are short and simple, arranged in eight series longitudinally, 

 or in four pairs in each segment. The two setaa composing each 

 ventral pair are nearer each other than those of the dorsal pair. From 

 segment XXI posteriorly, each seta is furnished at its side with a 

 shorter accessory one. No penial setas are found in the neighborhood of 

 the genital apertures. 



