290 W. WESCHE ON THE PROBOSCIS OF THE BLOW-FLY, 



Fig. 2). We have several good examples in various degrees 

 of development in our British fauna. Of the first, Drymia 

 hamata, Fin., seems to be the most archaic form, as it has an 

 older type of wing-venation than that which is found in the 

 Blow-fly ; apart from this, the proboscis is proportionately much 

 less elongated than in the case of several species of Siphona and 

 in Prosena, where it is nearly as long as the thorax and abdomen 

 together; and in the blood-suckers, judging from the venation of 

 the wings, we find a type which developed later than Drymia and 

 earlier than Siphonia in Stomoxys and Haematobia, and in the 

 exotic Lyperosa, whilst the African Tsetse flies (Glossina) show by 

 the wing- structure and in many other points of anatomy that they 

 are a later specialisation even than Siphona. Now the specialisa- 

 tions of the mouth follow these two types so closely that they might 

 be thought to be reliable signs of affinity, although the venation 

 of the wing would suggest that these specialisations took place at 

 different periods of time ; this is, however, not absolutely certain, 

 as the venation may have changed with the specialisation, 

 though, since I have shown that the two types of mouth have 

 four, or, if we include Madiza, even five types of wing-venation, 

 this seems highly improbable. I therefore think that these 

 specialisations are on parallel lines of evolution and have gradu- 

 ally been adapted to meet the exigencies of each case. Additional 

 probability is given to this suggestion by the fact that, in most 

 large families, specialised types of mouth are found, which are a 

 departure from the prevailing form ; insects such as Orthochile 

 in the Dolichopopidae, or Rhingia in the Syrphidae, are cases in 

 point. Also in some of the Acalyptrate Muscidae, small species 

 occasionally develop a long styliform proboscis, adapted for 

 probing the finer tubes of flowers. In a family of which one 

 species is probably familiar to most of us in the form of the 

 cheese maggot (the larval form of Piophila easel, L.), an adaptation 

 of this kind is found, namely in Madiza glabra, Fin. ; but, as I 

 have shown, this is no sign of relationship, but modification on 



