ENEMIES OF APHIDES. 125 



cellulose cases of the pollen may be somewhat similar to that of 

 the bran of brown bread or the husks of oatmeal when either of 

 these are ingested by man. 



Mr. J. W. Morris, F.L.S., has kindly endeavoured to identify 

 for me the pollens found in the viscera of Syrphus luniger, Rhingia 

 rostrata, and Erisialis tenax, and the result is, I think, a very 

 remarkable addition to our stock of knowledge in this direction. 

 These three species differ materially from one another in their 

 characters and habits, and the specimens examined were taken on 

 hedgerows or in gardens some miles apart. But two pollens were 

 found always present, accompanied by a third in a few instances 

 and in small numbers. The difference in appearance which may 

 be due to the liquids of the stomach necessarily makes precise 

 recognition difficult, if not impossible, and I think, myself, that 

 there is room to doubt whether this apparent third variety may not 

 be the result of partial digestion. At any rate, no more than three 

 pollens at the most are found, two of which are, without much 

 doubt, the pollen of some species of Doronicum^ or " Leopard's 

 bane,'" varieties of which bloom from spring to autumn, and that 

 of some near allies of Lathy rus^ of which the Everlasting Pea and 

 the Bitter Vetch are examples. These are shown at Fig. 3 on 

 PI. VIII., together with the other variety. 



As the flies visit in succession numerous flowers apparently for 

 food, it would seem that from among them all they select the 

 pollen of these or of nearly allied species, thus exercising a dis- 

 criminatory power which I am not aware has been similarly 

 observed among winged insects, and which, when confirmed by 

 other observers, will add to our estimate of the high degree of 

 intelligence already claimed by naturaUsts for the Insecta. 



The fact that the outer shells of these minute grains pass 

 through the fly in so perfect a condition as often to present no 

 serious difficulty in their identification, raises some interesting 

 questions as to the nature, the process, and the secretions by which 

 digestion is accomplished. In order to study this, it will be desir- 

 able for a moment to consider the composition of pollen. 



The grains of pollen consist of an outer case of considerable 

 hardness, which appears to be mainly cellulose, and which con- 

 tains the protoplasmic mass known as "foyilla." The hard case 



