NO. 12 FLYING APPARATUS OF BLOW-FLY — RITTER 33 



and whose wing-veins are very delicate, have no devices of this 

 kind to prevent jerks during flight. At every rapid change in the 

 direction or velocity of the wing-movement considerable stresses 

 must be produced, particularly in its basal part. The ill effects 

 which these might otherwise have are avoided by the flexibility and 

 elasticity of the wing which bends more or less at every stroke. If, 

 as in the Syrphidae, the wings are narrow and long, and the elas- 

 ticity of the veins is sufficient to permit such bending, there is no 

 special flexible zone. If, on the other hand, as in the blow-fly, the 

 wing is short and broad and the veins are hard and inelastic, a 

 special flexible zone is developed (pi. 6, figs. i8, 19, si) . This view 

 is supported by the serial instantaneous photographs made by von 

 Lendenfeld (pi. 19, fig. 53), which show that just after the down- 

 stroke the distal portion of the wing is markedly bent. 



It was not possible to ascertain the function of the curiously shaped 

 processus ptcralis thoracis V. Apparently this process can be inter- 

 posed like a stop between pterale C and the socket of processus 

 pterale alse 3, and so hinder the buffer action of pterale C. 



The processus pterale thoracis III as well as the processus pteralis 

 thoracis I are articular connections. Parts of them are poor in 

 chitin and therefore flexible, and they are firmly attached to the 

 parts of the skeleton to which they belong. 



I consider pterale B as a piece that serves to strengthen the joint. 

 Like a clasp it aids in holding the upper and lower portion of th(} 

 joint together. 



The numerous small folds in the anal portion of the wing, already 

 mentioned in the anatomical part of this paper, may serve to 

 strengthen this region, which is but little supported by veins. This 

 part of the wing is comparable to a Japanese paper fan, in v/hich 

 firmness is attained by radial folding. 



IV. SYNOPSIS OF RESULTS 



1. The constituents of the wing-joint can be divided into three 

 morphological groups, quite distinct from each other: 



1. The processus pterales thoracis. 



2. The pteralia. 



3. The processus pterales alse. 



2. The wing- joint is an exoskeletal structure, and therefore funda- 

 mentally different from the articular structures of vertebrate animals. 



3. This difference is chiefly due to the fact that in insects the 

 flexibility of the material permits some relative movement of differ- 



