Si,p t . 1890.] THE YOUNG NATURALIST. 161 



INSECT MIGRATION AND D. GALII. 



By W. E. SHARP. 



Mr. Tutt's article in the August part of this Magazine seems to 

 require some reply from me. I will in consideration of the feelings of 

 the readers of the Y. N. make it as brief as possible, my original articles 

 appearing so long ago that they may well have been forgotten. 



It is well to condense controversy as much as possible, and narrow 

 to a minimum the points at issue. I think I am right in reducing Mr. 

 Tutt's paper to two points of difference from me, viz. : --he affirms 



(1) . That insect migration is a well known and proved fact. 



(2) . That such migration is the explanation of the periodic abundance 



of D. galii. 



Both of which assertions he assumes that I deny. 



Merely pausing to point out that holding a theory not proven, is 

 not tie same as d raying it, I proceed to consider the first proposition, 

 and it appears to me that this depends entirely on the meaning in 

 which the term migration is used. 1, in my papers, attached to it a 

 much more definite and restricted meaning than Mr. Tutt apparently 

 does. I do not of course deny, that there are certain movements of 

 large bodies of insects, changes of location, which may be termed mi- 

 gration, indeed I instanced the case of locusts. The marches of 

 many species of Ants, or the clouds of various Lepidoptera which have 

 often been observed at sea, are also examples of the kind. Such oc- 

 currences are accepted facts. So far we are agreed. What I think 

 we have no warrant for assuming, is that recurrent changes of locality, 

 definite as regards direction, and periodic as regards time ; which we 

 ffnd among birds, as the swallow, the fieldfare, and the curlew, (from 

 shore to moorland) ; among fish, as the salmon ; or among reptiles, as 

 the turtle. Such changes of location, directed as they are by instinct, 

 and having for their object the wellfare of the species or its offspring, 

 is the voluntary migration to which I referred, and if Mr. Tutt can 

 cite any parallel case among insects I should feel obliged if he would 

 do so, as I can think of none. A mere tendency to dispersion, such as 

 has perhaps given to Cavdni a world wide range, I contend is quite 

 another thing. And this difference, a little more consideration will 



