Zoology 79 



sometimes occur in numbers: the first-mentioned is stated to live upon 

 water-fowl and the latter is at least partially a fish parasite. Very htde 

 definite information exists, however, with regard to their hosts. 



TURBELLARIA 



Five species of flatworms occur in ponds and ditches, and two species are 

 to be found in running water. These latter, viz. Planaria alpina and 

 Polycelis cornuta, occur in springs where the temperature is low and varies 

 Htde throughout the year. They are regarded as relics of a former glacial 

 fauna which once populated the County. 



PORIFERA 



The two freshwater sponges, Ephydatia fluviatilis and Spongilla lacustris, are 

 prevalent. According to G. P. Bidder, the common species, E. fluuiatilis, 

 is to be found on wooden piles, lock gates, or under floating wood, in the 

 waters around Wicken. Spongilla prefers deeper and moving waters, and 

 may be found growing up from the bottom of the River Cam along the 

 Backs at Cambridge. 



