LA BELLA IN GLOSSL\A. 109 



of the teeth being identical with that of the transverse rows of 

 teeth), and lie close together. The upper distal angle of the 

 upper plate and the lower distal angle of the lower plate are 

 each produced into a triangular tooth {h and i) ; at the distal 

 end of the plates are tirmly inserted four very large teeth (k), 

 two on the median and one on each of the other plates, and these 

 six teeth are directed towards the distal end of the labella. The 

 skin between the insertion of the submedian teeth and the end 

 of the labium is membranous and scaly (/), and at the upper 

 margin bears a number of short, stiff setse (m) instead of scales. 



1 am inclined to think that a portion of membranous skin 

 has been invaginated from the end of the labella, and that in 

 material preserved in spirit, or at any rate in fresh specimens, 

 the labella would sometimes be found with the membrane 

 alluded to evaginated and easily visible. This assumption is 

 based on the fact that with transmitted light four very long 

 chitinous rods are easily seen between the outer and the inner 

 walls of the terminal portion of the labellum ; in Fig. 1 1 this 

 portion of the right labellum has been drawn as seen from the 

 outer side, and the rods are indicated by dotted lines (d). Each 

 rod is very long, and nearly cylindrical, with the distal end 

 rounded, and is articulated to a somewhat short and rather 

 thicker cylindrical foot. I am unable to decide as to what the 

 function of these rods may be ; they are hollow, but I could not 

 discover any aperture at the end, and if they were ducts from 

 glands a distal aperture must exist. I am therefore most 

 inclined to believe that these rods are sense organs. They must 

 be inserted in membranous skin, which is invaginated in the 

 dried specimens seen by me. 



The outer side of the distal half of the labella exhibits a 

 small number of holes in which set* have been inserted ; in two 

 of my species these setae had been broken off near the base, but 

 in Gl. fasca they were present as moderately short stiff spines, 

 directed outwards and partly backwards. In the last-named 

 species I have also found four very small, clear rods arranged 

 along the distal end of the labellum ; these rods are certainly 

 sense organs. 



In Tahanus, Asilus, and Calliphora the labium contains three 

 pairs of muscles : in Gltssina I could distinguish two pairs with 

 absolute certainty, and they till up the basal inflated portion of 

 tlie organ. One pair proceeds from the sides of the labium in 

 an oblique direction and forwards to the margin of the plate 



