THE CAUSE OF MIMETIC RESEMBLANCE. 585 



f.icfts of the nocturnal species, that it is possible to infer the 

 habits from the structure of the eyes. Thus the species of the 

 Longicorn genus Doliops (family Lamiida:), which closely resemble 

 weevils (see p. 596), are, judged by this standard, diurnal in their 

 habits. The case is all the more interesting, inasmuch as sucli 

 an eye-structure, such habits, and such, mimicry is quite ex- 

 ceptional in the group, the NipJionincs, to which the genus 

 belongs. 



The facts recorded above imply sucli a resemblance betw^een 

 the nervous systems and sense-organs of the various species as 

 ■will make them diurnal (or in some cases semi-diurnal) in their 

 habits. This constitutes a further grave difficulty in the way of 

 any explanation based on external or internal causes. If the 

 diurnal habits are supposed to be due to such causes, the vastly 

 increased complexity of the result is the difficulty. If the 

 resemblances are supposed to be thus produced only in the 

 species which are already diurnal, it is impossible to explain why 

 the external or internal forces are thus restricted in their 

 operation. 



It is hardly necessary to point out that the time and space 

 relationships, which are such a difficulty in the way of the other 

 two theories, are entirely necessary to the explanation based on 

 the theory of natural selection. If they did not exist it would 

 be overthrown. 



(11) The Besemhlances which Insects of various Orders hear to 

 those of another Order are 'produced in the most Diverse Ways. 



The most common types for mimetic resemblance are those of 

 tlie wasp and ant. These aggressive, abundant, and successful 

 forms are resembled by insects of various orders. Still more 

 interesting is the fact that the resemblance is produced in the 

 most varied ways. 



A superficial resemblance to stinging Hymenoptera is probably 

 more general and is brought about by smaller changes in Diptera 

 than in any other Order of insects. A fly which gains alternate 

 black and yellow rings on its body is at once suggestive of an 

 appearance presented by many common wasps. In more extreme 

 cases, the body gains a constriction presenting a strong likeness to 

 the slender petiole of the wasp's abdomen, there are changes in the 

 manner of folding and sometimes in the colour of the winces in 



