EXTERNAL ANATOMY. 25 



The Comstock-lS'eedliam system was invented by the former 

 author and elaborated by the latter. Though it must be admitted 

 that Xeedham's researches into the homologies of the veins, not 

 only in Diptera, but in other orders of insects also (especially 

 Neuroptera), are, so far as I am able to judge, perfectly consistent, 

 there seems no necessity to alter the almost universally adopted 

 names of tlie veins. Moreovei', the abbreviations used to de- 

 signate the veins in this new system of venation, such as, Cs 2, 

 R 4 + 5, M 1 + 2, and so on, can never convey the decisive mean- 

 ing of terms of obvious significance, such as, costal cell, marginal 

 cell, 1st, 2nd, 3rd longitudinal vein, &c., all of M'hich by their 

 very names at once define their position in the wings. Of :ill 

 recent systems of terminology I cannot but regard this one as 

 the least acceptable. However, in spite of wliolly disagreeing 

 with this system of venation, I must accord Mr. Needham every 

 praise for the excellent series of Tipulid wings published by him, 

 Avhich has been most invaluable to me during my present studies 

 in this family. 



It must be remembered that modifications to suit special forms 

 are almost imperative, whatever system of classification be adopted, 

 for it is obvious that since some wings are replete with veins, 

 whilst others have very few, it must be a matter of careful study 

 to decide which are the veins that persist in these latter cases. 

 It is not therefore merely a question of an arbitrary and artificial 

 naming of the parts at caprice. 



Osten Sacken may be quoted here with advantage : — " Thus, if 

 we force ui)on the Tipulid^ the terminology introduced originally 

 in the families of Diptera with a less developed venation, we meet 

 with inextricable difficulties. But there is no more reason for 

 doing so than for following the opposite course, adopting a 

 termiuologv for the TiPULiDiE first and forcing it afterwards upon 

 the MusciD.i:. It is perfectly arbitrary at which end of the 

 system of Diptera we begin to trace out the homologues of the 

 venation. This study of the homologies has two distinct aims in 

 view ; the scientific aim of showing that the ground-plan of the 

 venation is the same in all the families of the order, and the 

 practical aim of adopting a terminology for descriptive purposes. 

 We cannot carry out a terminology on solely theoretical grounds, 

 we will have to vary the details of it according to the peculiarities 

 of structure occurring in different forms, the main plan remaining 

 the same." 



2. Internal Anatomy.* 



" The special features of the internal structure of the Diptera 

 are the high degree of concentration of the nervous system 

 attained in some members of the order ; the expansion of the 



* Tlie works of Brauer, Brandt, and Kiinckel d'Heirulais are recommended 

 by Dr. Sharp to the student of internal anatomy in Diptera, Will iston lias 

 drawn largely on Kellogg, and the notes herein offered are compiled from this 

 source, tlie present writer never having studied the subject. 



