EKRANTIATE POLYC'HAETA OF JAPAN. 165 



show a length of 00 — 100 mm. and a breadth of 5 — 6 mm. 

 There is no indication of any change in the structure of para- 

 podia, in the setae or in the eyes. Nor does the posterior region 

 of body undergo shriveUing, as it does in Ceratocephale osaiücti/''' 



There can be no doubt, that the persistent condition of para- 

 podia and setae enables the mature worm to swim as swiftly 

 as in the immature stage. 



The sexes are easily distinguishable by the colour of the 

 worms. The females are of a deep green on the dorsal side 

 and of a greenish yellow on tlie ventral. The males are dor sally 

 light greenish yellow and ventrally pinkish white blending into a 

 deep pink at base of parapodia. 



This species comes very close to Nereis dlversicolor 0. F. 

 Müll., as compared with the descriptions and drawings of the 

 latter given by several authors (Malmgeex, Ehlers and Schröder, 

 &Q,.) and also with alcoholic specimens from St. Andrews 

 (Scotland) and from Foxfield in the Dudden estuary (England). 

 However, there exist some differences between the two forms, 

 mainly in the arrangement of paragnathi. Thus, in the Japanese 

 species the paragnathi in the \l\. and ^^1I1. division of the 

 proboscis are arranged in one continuous row (figs. 18), 

 wliilc ill N. diversicolov they are arranged in three or 

 four irregular rows (fig. ID) ; and moreover, the falcate 

 l)ri sties of the foi'mer are of a greater magnitude than 

 tliose of tlu^ latter (figs. 10 and 17). The eyes of N.japonka are 

 proxidcd will) a distinct lens in each, while tliere is no lens to be 

 fou 1 1(1 ill tliose of N, cersicolor. The breeding habit of the Japa- 

 nese won II also differs from that of N. dkerùcolov, with regard 



* IzvKA, A. — Observiitioiis on the Jivpunese Pnlolo, Ceratocephale osaicai (-Tom. Coll. Sd. Vol. 

 XV]I, Alt. II, I;m:{.) 



