240 



I. IKEDA : 



the anatomy and histology to be added to the excellent contributions 

 previously made by Montgomery and Böhmig to the knowledge of 

 Stichostemmn species. As regards the embryology, the limited supply 

 of the material necessarily made my observations very fragmentary. 

 The shortage was especially felt in dealing with the question of cell 

 lineage, a complete study of which seemed to promise very desirable 

 results of high importance. I will now briefly describe the new species 

 with respect to its external and internal organization, and then give 

 what observations I could make regarding its life-habits and the 

 segmentation of the eggs. 



Stichostemmn f/raiirfis n. sp. 



External characters. 



The worms (fig. 1, Plate IV), when freed from the mucous coat 

 and fully stretched, measure 25-35 mm - hi length and 1 mm, in 

 breadth. The head end is rounded and somewhat broader than the 

 tail end. The eyes in the adults always number six, forming three 

 pairs. As in other species of Stichostemma, the anterior pair are the 

 largest and the posterior pair the smallest, and the distance between 

 the first and second pairs is slightly longer than that between the 

 second and third. The relative position of the three pairs of eyes 

 may well be understood from fig. 2, which represents the anterior end 

 of a young and rather transparent individual 4 mm. long. In such a 

 young individual all the organs lying on the surface of head are fairly 

 distinctly visible in surface view. Thus, the paired cephalic grooves 

 {c. v.), which appear like two comparatively deep and strongly ciliat- 

 ed pits, are seen situated close but ve ntral Iy to the lateral margin 

 and just in front of the second pair of eyes. The rhyncho-stomodaeal 

 opening (r. s.) may also be distinctly seen as a small despression 

 situated slightly ventral to the tip of head. Besides these, there are 

 always to be recognized, though indistinctly in the adult, two conspi- 



