394 Mr Lamb, Venationdl Abnormalities in the Diptera 



were less than 20 cases of teratological conditions, most of which 

 are here figured. The famihes the author has principally dealt with 

 are all characterised by simple venation, roughly of the syrphid 

 or muscid type, in which the cross-veins are very few in number. 



These teratological conditions are either those of deficit or of 

 excess. The first is shown in Figs. 1 and 2; the former is the tip 

 of the wing of Platypeza dorsalis showing the absence of the lower 

 part of the fork to the fourth vein; such a break is sometimes 

 definitely specific as in the genus Cryptophleps (Dohchopids), and 

 on the other hand the presence or absence of such a fork may be 

 a matter of indifference; thus in the tachinid Rhacodineura antiqua. 

 the upward bend so characteristic of the family is normally absent 

 or represented only by a small fragment of the upper portion: 

 very rarely, as in one specimen in the Cambridge series, it is fully 

 developed on both sides. Mr Colbran Wainwright drew the author's- 

 attention to the fact that this bend is also normally absent in the 

 tachinids Actia frontalis and Phytojnyptera nitidiventris. Fig. 2 

 shows the wing of Oscinis nana, in which the second vein definitely 

 falls short of the costa, a very rare condition in flies. Such a non- 

 attainment of the wing margin is not uncommon for the parts 

 other than the costa, and may even be such a constant character 

 as to be helpful in determination of the family. Teratology by 

 deficit is however rare except as a definite character. In the above 

 cases it is normally bilateral, and one of the remarkable things is 

 that bilateral occurrence is quite usual and occurs in the next 

 series of cases, especially in those shown in Figs. 9 to 12, 



Teratology by excess takes three principal forms; the com- 

 monest is that of little hang- veins ("anhangs") which occur in 

 many places, for example on the second long vein as in Fig, 10 or 

 on the discal cell as in Fig. 3 which shows one on the discal cell 

 of a specimen of Ocydromia glabricula (Empidae) in which family 

 the only other recorded case of abnormal veins is that of the 

 Tachydromia mentioned arbove. These hang-veins are often present 

 normally as for example in Ernoneura argus (Cordylurids) where 

 the second vein has a regular row of them hanging from it, each 

 carrying a spot of pigment. It is also always present in some 

 species of Parhydra (Ephydridae) at the end of the second vein, 

 where it forms a little hook which is often quite constant for a 

 given species, though in others it is rather variable, or, in rare 

 instances, absent. The size of the hang-veins dift'ers greatly; in 

 Fig. 4 is shown one in an agromyzid which is doubled at the base,, 

 though simple on the other wing; here it is long; that in Fig. 3 is 

 smaller, while those in Fig. 14, the case to be referred to later of 

 Ptilonota guttata (Ortahdae), show various forms; the limit is when 

 the hang-vein degenerates into a httle hard spot on the vein, a 

 sort of local breakdown in its continuity. 



