28 ENTOMOLOGICAL NEWS. [February, 



Certain sense organs, supposed to be those of hearing, exist in 

 the first abdominal segment, and in the tibiae of the first pair of 

 legs in various insects (Grasshoppers). 



Organs of smell are believed to exist in the antennae of many 

 insects. 



Organs of taste are thought to be present in the labium and 

 maxillae of some insects. 



The antennae play the part of organs of touch to a great extent. 



The muscles of an insect are very numerous. They are slender, 

 faint yellowish fibres, transversely striated, not enclosed in sheaths. 

 They are arranged in correspondence with the segments of the 

 body wall and the joints of the appendages. 



The respiratory system in insects consists of air tubes, or tra- 

 cheae.* They have their external openings, called spiracles, or 

 stigmata, in the pleura of the thoracic and first eight abdominal 

 segments, one pair to each segment. The number of pairs is 

 thus never more than eleven, and is usually less. In the thoracic 

 segments, at least, the spiracles are situated in the peritremes, 

 and are usually guarded by hairs, or a chitinous piece, acting as 

 a valve. A short trachea runs inwards from each spiracle to a 

 large longitudinal trachea, one of which runs along each side of 

 the body. These two large tracheae are connected by cross- 

 tracheae, corresponding in position to the segments of the body 

 wall. From the two main tracheae and the cross-tracheae, nu- 

 merous branches are given off in all directions, to all parts of the 

 body, thus supplying the organs directly and not indirectly 

 through the blood as in vertebrates. So numerous are the 

 branches of the tracheae that they also serve to hold other internal 

 organs in position. 



The tracheae are sometimes dilated into air-sacs, which also 

 decrease the specific gravity of the insect. Air-sacs occur only 

 in images of flying insects, and not in larvae, or in images of 

 creeping insects. 



Aquatic insects breathe either (i) air which they take from 

 above the water's surface, or (2) air which is mixed with the 

 water. In the first case the insect carries, by its wings, or other 

 means, a bubble of air obtained at the water's surface; or, its 

 spiracles are prolonged into long tubes which reach to the water's 

 surface while the insect is below it. Insects breathing the air 



* See ENTOMOLOGICAL NEWS, vol. i, pp. 71, 141. 



