^/^i*"'] Searle, Gleanings of a City NaturalisL 75 



lens at the end of a cone, which is lined with a dark pigment 

 and ends in a tiny nervelet. All these unite into one large 

 nerve, connected with the ganglia or brain. In addition to 

 these compound eyes the fly has three small ocelli, or simple 

 eyes, placed in a triangle on the top of the head. The width 

 of the space on the top of the head between the eyes is greater 

 in the female than in the male. In the front of the head is 

 placed the antennae, which are the principal means of classifying 

 flies ; they are composed of four joints, the third of which is 

 very much enlarged. That these are sense organs there can 

 be no doubt, though whether of touch, hearing, or smell it is 

 not possible to definitely say. The first three joints fit into a 

 recess, and are generally out of sight, only the plumose end, 

 the arista, being visible. Microscopic examination of the 

 enlarged third joint reveals the fact that it is covered all over 

 with little sacs or cells closed by a membranous covering. 

 At the base of the joint are a few larger apertures which lead 

 into cavities furnished at the bottom with hairs. Now, it is 

 quite clear that these latter structures have to do with some 

 sort of sensation, since each cavity is connected with the brain 

 by a fine nerve. From their general analogy to the ear of 

 higher animals, and by comparing their form in different kinds 

 of insects, it has been inferred that they are organs of hearing ; 

 probably they are endowed with a special sense of which we 

 mortals know not. Situated on the under side of the head 

 is the extensible proboscis. It is adapted for the absorption 

 of fluid food. It tapers slightly from above downwards, 

 and consists of three parts. First, a truncated, cone-shaped 

 portion, called the rostrum, attached to the under side of the 

 head ; to the front of the rostrum is attached a pair of palps. 

 The second and lower half of the proboscis, which is called the 

 transtellum or proboscis proper, is narrower. On the front 

 of this portion is hinged a narrow triangular appendage called 

 the labium -epipharynx ; it covers a groove in which a hollow, 

 stylet-like tongue or hypo-pharynx lies. The proboscis is ter- 

 minated by the oral disc, or sucker, which consists of a pair 

 of lobes or labella, which, when distended, form an oval 

 structure, the two halves being united by a bead and groove 

 joint. The surface of each labella is traversed by about 36 

 small canals, the channels of which are kept open by small, 

 incomplete rings. Between these canals, which are called 

 pseudo-tracheae, on account of their ringed appearance, there 

 are a number of nipple-like openings, which are probably 

 gustatory sense-organs. The pseudo-tracheae converge into 

 a small oral pit. When a fly alights, say, on a lump of sugar, 

 you will see the proboscis protruded, when the tip will unfold 

 into two broad, fan-like leaflets. A small portion of the sugar 



