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THE YOUNG NATURALIST. 



their appearance, are truly indigenous, yet there are certain others, 

 including among them D. galii, which, although-they may breed here 

 occasionally, are not truly indigenous, and would in fact become en- 

 tirely extinct in a few years, unless recruited by wind-blown immi- 

 gration from the continent. 



Mr. Tugwell says that he most fully agreed with most of my former 

 paper, but as that paper was an attempt to entirely controvert such a 

 theory with respect to the species on which the discussion turns, I 

 can hardly understand in what sense he does so. I trust, therefore, 

 that Mr. Tugwell will forgive me for pointing out wherein I consider 

 his theory to be wanting. I cannot help thinking that it explains a 

 part only of the case, instead of all the facts. If the sole known locali- 

 ties for D. galii were the littorals of Essex and Kent his case would 

 have been a good one, but the crux of the whole question lies not there 

 but in the north, on the Cheshire coast, and the Scotch and Irish 

 shores. 



Mr. Tugwell contends that far more larvae were taken last autumn 

 in the south, than on the Cheshire sandhills. I am not concerned to 

 dispute that, although had the fact any bearing on the question I 

 should like to be informed, as material factors in the calculation, both 

 the comparative areas of growth of the necessary Galium, and also the 

 number as well as the capability of the searchers in the two districts. 

 Possibly, for example, were Mr. Tugwell and myself to set out for 

 the same sandhills, his superior perseverance and sagacity might 

 reward him with dozens of larvae where I should return with a hardly 

 got ten. But, I cannot see how a comparison of captures can affect 

 the question ; it is generally allowed that both imagines and larvae 

 occurred everywhere where we had any reason to expect them, in 

 much larger numbers last year than for many previous seasons. 



Now, if Mr. Tugwell believes that this abundance can only be 

 accounted for in the case of the south coasts by a foreign immigration, 

 is he prepared to contend that similar phenomena in the north-west, 

 in Ireland, and in Scotland, must necessarily be the result of the same 

 cause : if so, is he also prepared to face the difficulties which the theory 

 entails, and which I have briefly indicated in my former paper. But 

 if not, if he agrees with me that natural local causes and these alone 

 must be held sufficient, why deny to Kent what he allows to Cheshire. 



Mr. Tugwell has, however, introduced evidence which he thinks 

 supports his immigration theory, and this, to some extent, it undoubt- 

 edly does. I allude to the comparative size of the imagines, but I do 

 not think in the first place, that his premises are sufficiently complete 



