32 THE REPORT OF THE No 36 



outstanding nature of the surroundings is very marked in contrast to the general 

 habitus it is reasonable to believe that the whole fauna inhabiting such a region 

 will develop to a marked degree along similar or parallel lines, although the 

 method of combating strange conditions may not manifest itself in the same 

 way. Still, a similarity must be expected. 



I have said that environment is changed by the modifications it produces. 

 All the laws of nature move in cycles and environment is no exception although 

 exactly similar conditions may not recur. Nevertheless they may approach 

 each other closely, and thus cause development along lines similar to those which 

 previously existed, and we may thus find insects receiving very similar stimuli 

 at widely divergent periods and developing much the same characters, although 

 their ancestors may have been distinct, but closely related, species, and those 

 forms resulting from the somewhat similar environment may resemble each 

 other closely. At any rate we should have two distinct series of insects developed 

 along parallel or similar lines, many of which would resemble each other much 

 more closely than did their ancestors, or more closely than they themselves 

 and their ancestors. 



It will be seen that it is therefore impossible to devise a lineal classification 

 of insects from either the imagines or immature forms, but at the same time it 

 must be realized that much reliance can be placed upon lineal descent, probably 

 in the majority of cases. This applies especially in what we are pleased to term 

 the families of insects, but becomes more obscure and less reliable as the groups 

 are enlarged, until, when we reach the orders and consider the near relatives 

 of insects we must trust entirely to deduction. I say this notwithstanding our 

 ever increasing knowledge of fossil forms, a complete understanding of which 

 is necessary in order to arrive at definite conclusions. These forms, their relation- 

 ship to each other and the changes manifest in the various strata in which they 

 are found will eventually lead to a more or less definite understanding of the 

 environmental conditions, and the changes in these conditions which influenced 

 and produced the stimuli causing insect modifications. 



It is, I think, an indication of progress when we are able to attain a classi- 

 fication of the adult forms of any family which corresponds as well to the larval 

 classification. It seems that we have reached this condition in the Syrphidae, 

 and while much still remains to be done, and several discordant factors are 

 apparent, it is a matter of great satisfaction. No group is better adapted for 

 such study nor does any family present such a diverse and yet remarkably 

 consistent group of characters from both the biologic and taxonomic aspect. 



Speaking generally, we have now grouped the genera in such a way that 

 all the Aphidophagous (species predaceous upon aphids), all the wood-boring 

 larvae, (the short-tailed maggots) and all the liquid or semi-liquid feeding larvae 

 (long-tailed maggots) fall naturally together. There are of course, as must 

 be in the case, exceptions. The remaining groups are varied in their habits. 

 Some species live in the nests of ants and termites, others in the nests of bees. 

 Those in which the larvae are dwellers in ants' nests form a compact group. 

 In the case of the second group, the adults form a moderately homogenous group, 

 but the larvae are very diversified in habits: some live in bees' nests, while, so 

 far as is known the majority bore in juicy plants, although it is by no means 

 certain that healthy plants are attacked. I have observed many adults of one 

 of these species (Volucella fasciata Macq.) about cactus plants in Kansas and 

 all the plants visited by the females had been previously injured by other insects. 



Among the Syrphidae which contain almost all the aphid eating larvae 

 I have found it practically impossible to distinguish several of the adults with 

 certainty, but the larvae are wholly different. In one case (S. americanus 



