October 13, 1893.] 



SCIENCE 



199 



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ON THE SYSTEIVUTIC POSITION OF THE DIPTEEA 



BY ALPHEDS S. PACKARD, PEOVIDEISICE, E. I. 



While, on the whole, the classification of the insects has 

 become of late years placed on a more scientific basis, 

 there is still some difference of opinion as to the syste- 

 matic position of the Diptera, a few authors regarding 

 the order as being the "highest," and entitled to stand at 

 the head of the insect series. 



Three important steps in the classification of insects 

 have recently been taken. (1) The higher position given 

 to those orders with a complete metamorphosis over those 

 whose development is direct ; no doubt the process of 

 metamorphosis is an adaptive, secondary feature, and one 

 not possessed by the more primitive, "lower" orders, such 

 as the Qrthoptera and Hemiptera, not to speak of the 

 Synajjtera (Thysanura, Cinura and Collembola). (2) The 

 next great advance was the dismemberment of the Pseudo- 

 neuroptera into a number of distinct orders, and the sepa- 

 ration of the metamorphic Neuroptera from the ameta- 

 morphic orders, with which they were formerly associated. 

 (3) The last stejJ in advance was the recognition of the 

 inferior position of the Coleoptera compared with the 

 Lepidoptera, Diptera, and Hymenoptera, the beetles hav- 

 ing been during the first half of this century universally 

 placed at the head of the insect class, for no other reason 

 apparently than that they were the favorites of entomolo- 

 gists. Even now Brauer j)laces them above the Lepidop- 

 tera and Diptera, but this seems to us to be erroneous, the 

 beetles in their adult structure, especially the Staphyl- 

 inidfe and Carabidse being not so far removed from the 

 Campodea-form type as the other metamorphic orders. 

 With Brauer we regard the Staphylinidse as being the 

 most primitive group of beetles, and near them are the 

 carnivorous groups (Cicindelidfe, Carabidse, Dytiscidse, and 

 other Adephaga). Indeed, instead of considering the 

 Ehyneophora as the " lowest," and therefore most primi- 

 tive group, we are now strongly disposed to regard that 

 group as neither "highest" or "lowest," but as the most 

 highly modified of all beetles, and therefore as a whole 

 probably more recently develojied than the bidk of other 

 Coleoptera. We would in classifj'ing the Coleoptera be- 

 gin with forms like the Carabidse and Staphylinidse, 

 because their larvae are the most in'imitiveof coleopterous 

 larvae, i. e., most campodea-shaped ; and the imagines are 

 more like their larvae than any other beetles, differing 

 mainly in having wings. Hence the Staphylinidse and 

 Adephaga are much nearer the ametamorphic Dermap- 

 tera and Qrthoptera than the Ehyneophora, or beetles 



like the Lamellicorns, Cerambycidae, Buprestidae and other 

 wood-boring Coleoi^tera, whose larvae are either footless 

 or tending to become so. Considering the larvae alone is 

 is evident that the carnivorous and leff- eating forms, with 

 flattened bodies, and well-developed legs, living a free, 

 active life, neither boring into wood or other vegetable 

 substances, but living under stones, or in the water, or on 

 the surface of leaves — it is evident that these are the earli- 

 est forms, and that the larvae of the Ehyneophora with 

 their cylindrical, apodous bodies are much later, adaptive 

 forms, which have lost their legs by disuse. The links 

 connecting them with the earlier beetles are the Bruchidae, 

 for example, which in their first larval stages have long, 

 well-developed legs, but which afterwards drop them, in 

 adaptation to their weevil-like life in peas, beans, etc, 

 The terms " high " and "low " are somewhat misleading, 

 and for them should be substituted the expression more 

 or less modified, or differentiated, recognizing the fact 

 that the "lowest" forms are usually the more generalized 

 and least differentiated, and especially least modified. 

 When forms are rendered "low" by parasitism, they may 

 be said to be degraded, retrograde or degenerate. 



Now the same views will, we would suggest, apply in 

 dealing with the Diptera. Compared with the Hymenop- 

 tera they are certainly more highly modified, but in a 

 more or less special direction. The Hymenoptera are, it 

 is now generally admitted, the most complicated or spe- 

 cialized and most differentiated group of insects; while, 

 on the other hand, the Diptera appear to be a side branch 

 of the insect tree, and both degenerate in important char- 

 acters, and very much modified in others. 



In the Hymenoptera there is a wonderful differentiation 

 of the mouth-f)arts. Instead of the abolition of mandibles 

 (Simulium excepted) and a reduction and modification of 

 the maxillae, which we witness in the Diptera, the three 

 pairs of mouth-parts are not only very equably developed, 

 but the parts are further elaborated with different por- 

 tions specially adaj)ted for special functions. In the Dip- 

 tera the jaws are wanting, the maxillae usually much 

 reduced, while the labium is enormously developed and 

 highly modified. The trunk of Hymenoptera is divided 

 into three equally developed regions, while in Diptera the 

 mesothoracic segment is enormously developed, the pro- 

 thorax being aborted. In the Hymenoptera the wings of 

 both pairs are well developed, in the Diptera the hinder 

 pair have lost their function, as wings, and are greatly re- 

 duced and modified with the minute balancers, and more 

 useful, perhaps, as organs of sense than of motion. 



If we take into account, also, the differentiation of the 

 brain of Hymenoptera, their social life, nest-building hab- 

 its, the differentiation of the sexes, their high intelligence 

 and very complete metamorphosis, the Hymenoptera cer- 

 tainlj"- overtop the flies. 



The larvae of Hymenoptera are, except those of the saw- 

 flies, very much modified, but the simplest more modified 

 ones, those of ants, wasps and bees, are less modified than 

 the maggots of the Muscidae and allied groups. 



And here we should, as in the case of the Coleoptera, 

 reverse the usual arrangement of the Diptera. It is evi- 

 dent that a form like Simulium, in which the jaws are re- 

 tained (though microscoj)ic and in a rudimentary or 

 reduced condition), is nearer what must have been 

 the original, primitive Diptera than any other forms, 

 usually in our systems placed above this genus. For a 

 stronger reason the mosquito, especially the female, with 

 its equably developed mouth-parts, the mandibles and 

 maxillae being well developed, is nearest to what was 

 probably the earliest, most primitive, most equably differ- 

 entiated Diptera. In classifying the Diptera, therefore, 

 we should prefer to begin with the Culicidse as being the 

 most primitive unmodified Diptera, and end with the 



