COLLECTION OF BDELLOID AND OTHER ROTIFERA. 209 



rotifers of a very few species, but rather to secure representa- 

 tives of as many species as possible of those inhabiting the pond 

 at the time of collection. I prefer therefore a larger net, which 

 can be used not only for surface dipping, but also for deeper 

 work, as well as in larger bodies of water, where rotifers are 

 generally present in much fewer numbers. For this more general 

 use, I think that the depth of the net should be not less than 

 one and a half times the diameter across the mouth. When 

 collecting at a depth of several feet below the surface, it is easy 

 to turn such a net so that little water can enter it before it 

 reaches the desired depth ; it can then be opened fully, and 

 again closed before withdrawal. 



The diameter of the net has also some importance ; a very 

 small net-ring would be of little use in working large bodies of 

 water, or for the plant-washing methods employed by Murray 

 to which I shall presently refer. For general work I prefer a 

 ring of not less than six inches diameter, as large, in fact, as will 

 easily enter a side pocket, and an oval outline is perhaps more 

 convenient than the round. In these days the net material is 

 usually Swiss "bolting silk" of suitable gauge (No. 14 or 15), 

 but Harring (who also, I think, prefers a large net) has used 

 China silk, and I have found Indian silk fairly satisfactory. 



To the single net generally employed I have the objection that 

 it admits into the catch too many Entomostraca, larvae and 

 other unwelcome guests. I cannot affirm that I have at any 

 time seen Entomostraca attack rotifers, but I am certain that 

 they consume quantities of food which would otherwise be 

 available for the latter. If it is desired to keep the captured 

 rotifers alive, the Entomostraca, larvae, water-worms, etc., are 

 better left in their native pools. In recent years I have there- 

 fore made use of a double net of two different textures, the outer 

 of the customary material, and the inner of muslin sufficiently 

 close to act as a coarse filter to keep out, at least, the larger of 

 the objectionable intruders, while permitting rotifers to pass 

 through. 



This double net had, however, the disadvantage that it was 

 impossible to get at the " catch " unless the inner net was un- 

 attached to the net-ring on one side. I happened to mention 



