34 



small tracheae. Carefully trace out the courses of the small 

 tracheae and represent them in your drawuig. 

 3. A spiracle. 



INTERNAL ANATOMV. 



Preliminary work. — Take from the chloral hydrate 

 solution a specimen which was slit on the ventral surface. 

 Immerse the insect in water, with its dorsal surface down- 

 wards. With fine scissors extend the slit the whole length 

 of the thorax and abdomen ; in making this slit cut through 

 the wall of the body into the perivisceral cavity ; the body- 

 wall consists of two parts, the external crust of the insect, 

 and, entad of this a wall of muscles; it requires consider- 

 able care to cut into the perivisceral cavity and not injure 

 the viscera. Make, on each side, in that part of the body- 

 wall connecting the prothorax with the head, an incision 

 extending from the longitudinal incision to the side of the 

 body. 



On the meson just entad of the ventral wall of the body, 

 there are two white cords, extending nearly the whole 

 length of the body. At intervals, which approximate the 

 segments in length, these cords are united ; at the points of 

 union they are greatly enlarged ; from these enlargements 

 there arise numerous, small, white cords, which extend in 

 various directions. The two longitudinal cords, the en- 

 largements upon them, and the numerous cords branching 

 from these enlargements constitute the nervous system ; the 

 cords are nerves and the enlargements are ganglia. The 

 nervous system will be studied later in a specimen which 

 has been opened on the dorsal side. 



Cut away from the ganglia the nerves that extend to one 

 side ; do this with the scissors, first placing one blade under 

 the nerves and lifting them away from the other viscera. 



Take a strip of sheet-cork a little longer than the insect 



