228 ME. W. WESCHE ON THE LABIAL AND 



developed, and the tegulse small or absent. This might be an ancestral or primitive type 

 of the Muscidae. 



Tolietes and Hyetodesia would only differ from this insect by less developed maxillary 

 palpi, a longer labium, and larger tegulse. Ophyra leucostoma, while retaining the short 

 labium, has lost the plumose arista, the hairy eyes, and retains fairly large rudiments 

 of the palpi. Cyrtoneura has also lost the hairy eyes, developed a slightly longer labium, 

 but retains the plumose arista and fairly large rudiments of the palpi. 



In Hydrotea the palpi are present, but the plumose arista has gone. Some species 

 retain the short labium, and others have lost the pubescence on the eyes. Einally, we 

 come to the little Lasiops, with haii'y eyes and only rudiments of the maxillary palpi. 



My diagram is drawn up on this system — that is, as the species lose primitive 

 characters they become more recent ; and it would be tedious to trace the matter further, 

 as a glance at the scheme will make my meaning clearer than any written explanation. 

 (Plate 10.) 



Classification. — It will be seen that this arrangement shows what excellent natural 

 groups the species of the Anthomyiidse and the Muscidse have been divided into, and 

 how one character more, the rudimentary palpi, follows the order in which the genera 

 have been placed. It is well marked in the subfamily Mydaeinse, dwindles in the 

 Anthomyiinse and Homalomyiinse, disappears in the Coenosiinse, and no trace is found 

 in the nearly related Scatophaga. 



In this paper I have endeavoured to avoid a controversial attitude, but it must be 

 obvious that if the conclusions I have arrived at are correct, the contrary must be the 

 case with the works of several theorists, and that the generally accepted dogma that the 

 palpi in Diptera are homologous and maxillary can no longer stand. Therefore it will 

 probably be urged by some (and, looking at the subject from their point of view, I admit 

 quite fairly) that my methods are out of date, and that comparative anatomy must give 

 way to a minute sectional study of the insect from the ovum, through the metamorphoses, 

 to the imago state. To this I answer that this method, so apparently promising and 

 conclusive, when applied to the trophi of Diptera, is discounted by its results. Either 

 it is a tool of such complexity and nicety that no observer has hitherto used it correctly, 

 or the facts observed have not been properly weighed and understood. 



Since the preceding pages were written. Professor V. L. Kellogg has published a paper 

 which lends valuable aid to my contention as to comparative anatomy and ontogenetic 

 study, when applied to the homologization of the mouth-parts of Diptera *. 



If the presence of labial and maxUlary palpi in Diptera is admitted, and I cannot see 

 how, unless my facts are traversed, this can be denied, such speculations as the derivation 

 of the labella from the fusion of the labial palpi or from the fi7^st maxillae cannot 

 be entertained, though my investigations quite agree with the theory that the labium is 

 a modified double maxiUa, derived from the second pair of jaws. 



* " The Development and Homologies of the Mouth-parts of Insects," The American Naturalist, vol. xxxvi. 

 (Sept. im-Z), pp. 683-706. 



