Mr Lamb, Venational Abnormalities in the Diptera 393 



Venational Abnormalities in the Diptera. By C. G. Lamb, M.A. 

 [Read 7 March 1921.] 



The pubHshed records on this subject are very scanty, only 

 two or three notes having appeared for many years past. The 

 most remarkable case on record is described and figured by F. W. 

 Edwards {Entomologist's Monthly Magazine, 1914, p. 59). It is 

 that of a tachydromid in which the simple venation natural to 

 that genus suddenly flourished out into a highly complex and 

 irregular network of cross- and accessory-veins, which show nearly 

 every form of abnormality that the wing can be afflicted with; 

 this physiological explosion remains unique. Dr Keilin records a 

 case of true malformation, in which the distal part of both wings 

 is greatly abbreviated and deformed, in the Bnll. Soc. Ent. France, 

 1917, p. 194, and suggests that the condition has been brought 

 about by pressure. The abnormahties which are now referred to 

 are usually smaller and more regular, and are scarcely striking 

 enough to be called teratological, but as there is apparently no 

 definite boundary between the two sets of cases, that term will be 

 used for convenience. 



The only recently pubhshed matter bearing on the abnorm- 

 alities to be considered is contained in three short papers by 

 Krober published in the Zeitschrift fur Insekten Biologie in 1910, 

 where several cases similar to the following were figured, these 

 will be referred to in passing. Apparently the above include all 

 that has been pubhshed on the subject of wing teratology though 

 there are several scattered notes on antennal teratologies. 



Abnormal venation is naturally more probable in those flies 

 which have an approach to the generahzed Panorpa-like venation, 

 both from the greater number of the veins and from the presence 

 of two possible stress systems at right angles, and consequently 

 it is not surprising that Mr F. W. Edwards of the British Museum, 

 who has had an exceptionally intimate knowledge of the Nemato- 

 cera, informs me that he has frequently seen aberrations in the 

 venation of that section, and that they are particularly common 

 in the tipuhd genera Eriocera and Tricyphona. On the other hand 

 Mr J. E. Collin considers flies to be remarkably free from wing 

 abnormahties, and that they occur only in "certain species such as 

 the one to be referred to later on. The author's experience is practi- 

 cally confined to the non-nematocerous families and agrees with 

 that of Mr Colhn. Neglecting one exceptional species, among the 

 many thousands of individuals that have passed before him, there 



