. 
> 
156 The Proboscis of the House-fly. [March, 
On both sides of the mouth are hard beams of chitin, sup- 
ported on the trabeculoid processes of the axis piece of the mid 
segment (Fig. 3, xt), and themselves affording a foundation for 
the false tracheæ. We shall call them the circum-oral rods (Fig. 
1, F). On the circum-oral rods, and intervening between the 
roots of the false tracheæ, is formed a set of teeth. The blow- 
fly has three rows of these teeth (thirty teeth in all), each tooth 
being two-cusped. A small house-fly (similar to M. domestica) has a 
similar arrangement, as has Musca cesar. The carnivorous house- 
fly has only one row of five or six teeth on each side of the 
mouth, but the teeth are three-cusped, the cusps being more or 
less cut (Fig. 1, Hand F). The blow-fly has been found to use 
its teeth for scraping sugar-candy. 
I would suggest that these distinctions in the structure, num- 
ber and arrangement of the teeth are of generic value, and that 
the name Musca be applied only to those species having a single 
row of three-cusped teeth; whilst Calliphora, already made to 
include the blow-fly, should take in those having several rows of 
two-cusped teeth. 
On the distal end of the mentum gi the mid segment, are two 
elastic chitinous bands, clasping the tip from behind. When these 
bands are pulled apart by muscles inserted in the mentum, they 
open the lips wide. Muscles and tracheæ are variously distrib- 
uted throughout the proboscis. At base of the tip is a nervous 
ganglionic mass which sends fine filaments to small terminal 
ganglia at the lower extremity of the lips, two of these ganglia 
being borne on the dichotomous branches of each nerve-pedicel. 
` The surface of the proboscis supports hairs at various parts, espe- 
- cially on the palps and at the tip. The tip itself has no muscles; 
it is tumid but not fleshy. 
The proboscis of the blow-fly and other Muscidæ corresponds, 
except in detail, with that of the house-fly. The proboscis of the 
piercing-fly (Stomoxys calcitrans) has not the swollen tip, and its 
sheath is converted into a brown annulated tube, split above. Its 
basal part is retractile and exactly as in the house-fly. Its oper- 
cular piece, hypopharynx and axis piece are much elongated, as a 
piercing rather than a merely suctorial apparatus. In many points 
the oral apparatus of the mosquito corresponds so closely with 
that of the Muscidæ, as to render valpabk help towards the inter- 
EES of the latter. 
