TklCLAD TURBELI-ARIA FROM INDIAN TIBET 11 



Of the three specimens, the smallest (Plate II, fig. 6) has four eyes of ec|ual size, the medium- 

 sized one (Plate II, fig. 7) has two eyes of regular size in front of which are two small eyes, 

 and the third, the largest, has one small eye in front of one of the two regular eyes (Plate II, 

 fig. 5). It is possible that in this form the eyes are regularly replaced and the small eyes of 

 Plate II, figs. 5 and 7, represent new eyes in process of development. However, the pres- 

 ence of supernumerary eyes is not at all uncommon in planarians and cannot be used as a 

 taxonomic character. 



Affinities 



These species appear to resemble American forms more nearly than they do European 

 planarians. The European Polycelis species have a single row of eyes along the anterior 

 margin while the banded arrangement, several eyes wide, occurs only in Asiatic and American 

 forms. In the eyes as well as in the anatomy of the copulatory apparatus Polycelis tibetica 

 bears considerable resemblance to Sorocclis sapporo (presumably a Polycelis) of Japan 

 ( Ijima and Kaburaki, 1916). Also the Euplattaria (?) of the present collection is very 

 like some common Euplanariae of the United States while differing from European Etiplan- 

 ariae. .Altogether it would seem that the Asiatic species have spread toward North America 

 (or vice versa) rather than toward Europe. 



