A NEW FRESH-WATER NEM ERTINE. 



2-19 



being apparently entirely idiosyncratic. It is, of course, a well known 

 fact that the number of proboscis-nerves is in many other groups of 

 nemertines variable to some extent even in one and the same species ; 

 consequently, it cannot be much utilized for systematic purp se. 

 This seems however not to apply to the three hitherto known species 

 of Stichostcmma, in which the number is definitely known to be either 

 9 or io. This fact has induced me to regard the indefiniteness in 

 the number of proboscis-nerves in the present species as one point of 

 its specific peculiarities. 



Lastly, the remarkably large size of the present species deserves 

 special mention, as this seems to be correlated with several important 

 characters of the species, for instance, with the unusually large 

 number of mature gonads, with the comparatively short extent of the 

 rhynchoccel, etc. From what I have described in a previous para- 

 graph, it will readily be seen that the characteristic points just referred 

 to undergo more or less remarkable changes, according to certain stages 

 of growth, even after the animals have actually entered into sexual 

 maturity. While the maturing gonads increase in number as the 

 animals grow larger, the cephalic glands and the rhydchocoel tend to 

 become reduced in their relative range of extent. So that, if the 

 worms in widely different stages of growth be obtained from different 

 localities, it would be more or less puzzling to determine whether or 

 not they should be brought under the same species. It is interesting 

 to notice that the four species, if arranged in the order cf their body- 

 lengths, as they are in the foregoing table, seem to show between 

 them certain relations similar to those which I have pointed out in 

 the present species with reference to different stages of its individual 

 growth on the one hand, and the number of mature gonads and the 

 relative extent of cephalic glands on the other. If this idea be cor- 

 rect, an explanation suggests itself why the two such remotely related 

 species as St. asensoriatum and the present species show the singular 

 agreement in having cephalic glands of a similarly low develop- 



