MICROSCOPIC OBJECTS. 



Fig. 139. Spiracle of Larva of the Death? s-Head Hawk- 

 Moth ( Acherontia atropos) , x 20. 



The spiracle of the larva of this moth (which is generally 

 found on the potato-plant) may be taken as the general type 

 of the spiracles of most of the larvae of the Moths and Butter- 

 flies. On dissecting any larva, a number of minute tubes, 

 greatly resembling the spiral vascular tissue of plants (see 

 fig. 16), will be found leading to each spiracle or breathing- 

 pore; these tubes or tracheae are figured in the following 

 drawing. 



The spiracles, when cut away from the side of any larva, 

 must be soaked for a short time in diluted potassa fusa as 

 usual, then well washed, dried under pressure, soaked in tur- 

 pentine, and mounted in balsam ; or they may be mounted 

 in a shallow cell in acetic acid. 



Fig. 140. Tracheae of Silkworm (the larva o/Bombyx mori), 



x40. 



Tracheae of all insects resemble each other in structure, 

 although differing greatly in size. They are best seen when 

 taken from any of the larvae of the large Moths or Butterflies. 

 They consist of tubes greatly resembling the spiral vascular 

 tissue of plants (see fig. 1 6), and, like the components of this 

 tissue, they may be uncoiled. These tubes lead to the air- 

 pores, or, as they are called, the spiracles (see figs. 122, 139, 

 154, &c.) of insects, and serve to conduct the air to all the 

 central parts of the body. 



The tracheae show best when mounted in fluid, although 

 they may be dried and mounted in balsam. 



