TWO AQUATIC OLIGOCHiETES. 47 



than in L. gotoi. These differences in the development of these 

 organs may perhaps furnish a clue to their function ; for it seems 

 to me that they are larger during the active season of the 

 animal. Locality and climate or temperature are also factors to 

 be considered ; for in none of the Tokyo specimens of this 

 species have I observed septal sacs of such size as is figured by 

 Stephenson, although some of these specimens were larger than 

 any from Ceylon. At any rate, it is interesting to observe that 

 the condition of the septal sacs in the summer specimens of Tokyo 

 is the same as in the winter ones from Ceylon. It may be that 

 L. socialis Stephenson represents older specimens of L. gotoi, 

 which are either scarce or not found in Tokyo. 



As to the sinus-like blood space especially described by 

 Stephenson as being present in segment IX, I am of opinion 

 that it must be inconstant, for a reexamination of my sections 

 shows it to be absent. 



March 16, 1913. 



