On Synchci'ta fennica sp. n. By Charles F. Rousselet. 173 



& stylata and grandis are rare forms ; the first I have occa- 

 sionally, whilst the latter I have never, found in the canal. The 

 periodic and often very sudden, disappearance and reappearance of 

 various Rotifers is a well known fact, and the Synchzeta follow the 

 same habits. 



I am quite prepared to admit that iu large lakes there may 

 exist some seasonal variation in the direction of elongation of 

 body or increase in length of spines in some species, not, however, 

 in effecting such structural and organic changes which would 

 convert a Synchieta oblonga into S. pectinata and that species into 

 S. stylata or S. grandis. 



