214 DAVID BRYCE ON THE 



is the examination of sucli animals as Asellus and Gammarus, 

 Nepa, Caddisworms and all kinds of larvae and water-worms, 

 and of various algae for those species of Rotifera which infest 

 them either as a source of food, as a means of transport or 

 merely as a shelter. It would occupy too much time and space 

 to enter into particulars of the various grades of parasitism 

 shown by such Rotifera. It suffices to say that some, indeed 

 most of them, are of the most interesting nature, and that here, 

 as in other matters, " it is the unexpected that happens." As 

 an instance of the " unexpected," I may mention the discovery 

 about fifteen years ago, by a young Italian student, in the course 

 of his studies for the Degree of Doctor, of three unknown species 

 of parasitic Rotifera in the gill-cavities and actually upon the 

 gills of the Freshwater Crab. Two of the species belonged to 

 the Bdelloida, and the third was a member of the genus Distyla, 

 a genus usually associated with weedy ponds and sphagnum bogs. 

 I think it is more than possible that if one of our younger 

 men would take up the study of parasitic Rotifera, as a special 

 line of investigation and in a systematic fashion, he would make 

 some very interesting and valuable discoveries. In the case of 

 Asellus and Gammarus, nearly every individual carries with it 

 several parasitic Rotifera, and the former animal is the usual 

 host for at least half a dozen different species. If an Asellus or 

 Gammarus be confined in a live box so that it cannot move 

 freely, the Rotifera will presently leave their positions. It is 

 then easy to remove the Asellus and to isolate the rotifers for 

 closer examination. Another method is to place several Aselli 

 or Gammari in a small, wide-mouthed bottle half filled with 

 water. The bottle is then well shaken, and the rotifers forcibly 

 detached from their hold. By pouring of! the water into a 

 stage trough, the rotifers, being carried with it, can be easily 

 picked out under the microscope and isolated. Asellus is usually 

 found among water-plants in weedy pools — Gammarus more 

 frequently in muddy ponds. In running water, however, the 

 latter can sometimes be found by lifting stones from the bottom. 

 Both of these hosts should be collected from as many different 

 localities as possible, and the results carefully noted for com- 

 parison one with another. The rotifers which are parasitic upon 



