The Food Relations oj the Carabidw and Coccinellida: 35 



sionallv, at least, bj the principles of natural selection, especially 

 as applied to the machinery of food prehension. Whatever 

 departure from the primitive vegetarian habit of animals any 

 group has acquired, was of course initiated to enable it to draw 

 on other food resources than those previously open to it. But as 

 animal food is usually less abundant and less generally distributed 

 than vegetable, it would not, at first, be to the advantage of any 

 that they should become exclusively dependent upon the former; 

 their interests would be best served by such modifications of 

 structure and habit as would enable them to draw upon one or the 

 other store, according to circumstances. Acquiring some power 

 to capture and masticate animal food, they would not wholly lose 

 that of appropriating vegetable food also; and however well fitted 

 their prehensile and digestive organs might become for the former 

 fuTiction, Ave should expect that they would not altogether lose 

 their fitness for the latter. It would be only as competition on 

 tliis higher plane increased to the pressure point, that a few mem- 

 bers of the differentiating group would be forced to the highest 

 plane of complete dependence on animal food alone. 



The first results of an attempt at a mon; exact and exhaustive 

 investigation of this svibject, were given by the writer in a brief 

 paper published in Bulletin 3 of this series, in November, 1880.* 

 In another paper by Mr. F. M. Webster in the same Bulletin,-!- ^ 

 summary of previously recorded observations was given, together 

 with many additional and original field notes. A few other items 

 have since been published by others, but confined, as far as known 

 to me, to chance observations on single insects. 



The method here followed, as in the paper above mentioned, 

 has been that of dissection. The alimentary canals of beetles 

 taken in a oreat variety of situations, at various seasons and at 

 different times of day, have been removed, placed in glycerine on 

 microscope slides, and opened with small knives and mounted 

 needles, so as to display the contents completely. These liave 

 then been studied with whatever power of the microscope was 

 necessary, and mounted as microscope slides for permanent pres- 

 ervation and repeated examination. The amount of information 



■■■Notes on Insectivorous Colcoptera. By S. A. Forbes. Illinois State 

 Laboratory of Natural History, Bulletin No. ;>, \)\>. Io3-160. 

 tPp. 149-152. 

 5 



