A NEW FRESH-WATER NEMERTINE. 245 



to maturity almost simultaneously. S> long as the egg-cells remain 

 in the earlier stages of growth and arc still attached to the gonad- 

 wall, no spermatid or spermatozoon is yet formed and the male ele- 

 ments arc represented by a few small masses of spermatogonia or 

 spermatocytes, nearly all of which show division-figures. Of course 

 these cell-masses still lie in the epithelium, mostly in close vicinity 

 of the funnel shaped mouth of the genital duct. In the eggs, the 

 later phases, during which they reach maximum size and are brought 

 to complete maturity ready for deposition, arc indicated : first, by 

 their liberation from the gonad-wall ; secondly, by rearrangement of 

 nucleoli from a localized disposition with tendency to accumulate at 

 the ventralmost corner of the germinal vesicle, into a regular periphe- 

 ral destribution ; thirdly, by the development of the two egg-membranes. 

 Nearly simultaneously with, or a little prior to, the processes 

 mentioned above, the spermatids make their first appearance, subse- 

 quently to undergo metamorphosis. This metamorphosis takes place 

 in some parts of a gonad a little earlier than the liberation of the 

 eggs, so that in many gonads there are to be seen fully formed free 

 spermatozoa in accompany with eggs which have not yet reached the 

 final maturation-stage. Nevertheless, the interval between the maturing 

 of the male and female elements is never so long as to cause protand- 

 ric hermaphroditism like that of St. eilhardi. 



So much for the more important characters of the present species 

 as seen from the systematic point of view. A brief discussion will now 

 follow regarding its systematic relations to the allied forms known. 



It will not be necessary to enter into a historical or critical 

 review of fresh-water nemertines, as this has already been thoroughly 

 done by Sillimaiv and more recently by Montgomery (1895) and 

 Böhmig (1898). Setting aside for the present the question of the 

 validity or non-validity of the several species that have hitherto been 



1) Silliman, W.A., Beobachtungen über Süsswasserturbellarien Nord-Amerikas. Zeif- 

 schr. f. Wiss. Zoai., Bd. 41, 1885. 



