Vol. XX vi] ENTOMOLOGICAL NEWS 7 



had built its case and was feasting on the diatoms about the 

 door of its house. This incident seems to express, perhaps 

 '^ iggcrated form, the one-sided benefit resulting from the 

 Miiship between epiphytes, epizoa and the nj-mphs. Kam- 

 merer (*o8), who maintained that the algal growth may bring 

 to the nymph such benefits as a richer supply of oxygen, the 

 keeping aloof of {)arasites. protection through color, et cetera, 

 thinks this relationship is one of symbiosis. The relation 

 seems to me to be a natural one resulting from proximity; 

 l)ecause, if the populations living upon the nymphs be com- 

 I)ared with those of the mud and water weeds which the 

 nvniphs inhabit, they will be found practically the same. The 

 abuiubnce of the (xjpulation in both cases depends to some 

 extent upon the inactivity of the UN-mphs. 



III. The Food of the Nymphs. 

 From Novemlier 14 to July 10, dragonfly and damsd-fly 

 n>inphs were taken from Cascadilla Pond directly to the labo- 

 ratory, where the contents of their stom.-i ' <• mounted 

 in water upon slices an»l examined under t: . o5coi>e. If 

 they could not be examined immediately, the heads of the 

 luinphs were removed from the bodies and the alimentary 

 caiKil gently pulled out. but not severed, so that the contents 

 could be preserved in formalin, and the head and body remain 

 connected for later identification. Eight n)'mphs contained 

 no fragments of food, but four of these had eaten much sand. 

 The presence of large quantities of diatoms* was puzzling 

 until it was noticed that they appeared during the cold months 

 when Chironomid lar>'ae are the chief source of food, and, in 

 one or two cases, they were seen to be protniding from par- 

 tially digested larvae. The cases of the Chironomids, on which 

 (liatoius L ' Tulantly. may account for some of the sheUs 

 and prob. sand present was that of Chironomid cases 

 from which the brvae had been entirely digested. Bits of 



*I )r. A. H. Morgan has soficsted that some of the diatoms are an- 

 iluubtcdly taken in with the mayflies since they arc abandant in the 

 food and epiphjrtes of mayfly nymphs. 



