24 ART. 11. A. IZUKA I OBSERVATION ON THE 



In both sexes, the segments of the thoracic region gradually 

 enlarge antero-posteriorly to about the 10th segment and then 

 remain nearly the same in size down to the abdominal region. 

 The parapodia of that region are essentially similar to those in 

 the corresponding body-part of immature worms (Woodcuts 5-6), 

 except in this respect that the dorsal and the ventral cirri are 

 generally much more slender and longer. The aciculse as well 

 as both the falcate and the setose bristles remain, in the thoracic 

 parapodia, in much the same condition as before. 



In the abdominal region, the segments begin again to gra- 

 dually broaden and continue to do so to about the 40th in the 

 female, and to about the 45th in the male ; then they narrow 

 backwards to the posterior end. The parapodia in this region 

 show a somewhat sudden enlargement within the anterior two or 

 three segments ; and after that they are seen to increase posteriorly 

 gradually in size until the 40th (female) or the 45th (male) 

 segment is reached. Beyond this thev again become gradually 

 smaller towards the hind end of the body. 



In all the abdominal parapodia (Woodcuts 7-8), the distinc- 

 tion between the dorsal and the ventral rami is more pronunced 

 than in the atocous stage ; the cirri are more elongated, and their 

 basal portion much shorter, being sometimes scarcely distinguishable 

 as such. The ligula has become somewhat more slender. The 

 " Spinndrüsen " now show a rounded outline. The extension of 

 the body-cayity into the parapodium is full of mature eggs or 

 spermatozoa according to the sex. Sometimes the sexual products 

 are found even in the interior of the ligula. The acicuhe present 

 simply a larger size in correspondence to the general growth 

 undergone by the parapodia themselves. 



In the anterior two or three abdominal segments, the paddle- 



