RESPIRATION IN INSECTS. 323 
buried among the muscles. Besides the ordinary air-sacs, 
there is in the end of the abdomen, behind the ovaries, a 
plexus of six dilated air-sacs (Fig. 282, I, II, III), which 
are long, spindle-shaped, and are easily detected in dis- 
secting. 
There is a system of dilated trachee and about fifty air- 
sacs in the head. 
In the legs two trachee pass down each side of the femora, 
sending off at quite regular intervals numerous much-branch- 
ing, transverse twigs; there is one large and a very small 
trachea in the tibia, and the main one extends to the ex- 
tremity of the last tarsal joint. 
By holding the red-legged locust in the hand, one may 
observe the mode of breathing. During this act the por- 
tion of the side of the body between the spiracle and the 
pleurum (Fig. 273, A) contracts and expands ; the contrac- 
tion of this region causes the spiracles to open. The gen- 
eral movement is caused by the sternal moving much more 
decidedly than the tergal portion of the abdomen. When 
the pleural portion of the abdomen is forced out, the soft 
pleural membranous region under the fore and hind wings 
contracts, as does the tympanum and the membranous por- 
tions at the base of the hind legs. When the tergum or 
dorsal portion of the abdomen falls and the pleurum con- 
tracts, the spiracles open ; their opening is nearly but not 
always exactly co-ordinated with the contractions of the 
pleurum, but as a rule they are. There were sixty-five con- 
tractions in a minute in a locust which had been held be- 
tween the fingers about ten minutes. It was noticed that 
when the abdomen expanded, the air-sacs in the first ab- 
a 281.—Showing distribution of air-tubes (tr: chez) and air-sacs—side view of 
the body. v, main ventral trachea (only one of the two shown); s, left stigmata) 
trachea, connecting by vertical branches with D, the left main dorsal trachea; ¢, left 
cephalic trachea ; oc, ocular dilated trachea. From the first, second, third, and fourth 
spiracles arise the first four abdominal air-sacs, which are succeeded by the plexus 
of three pairs of dilated traches, I, II, III, in Fig. 287. Numerous air-sacs and 
trachez are represented in the head and thorax. The two thoracic spiracles are rep- 
resented, but not lettered. 
Fig. 282.—D, left dorsal trachea; 3S, left stigmatal trachea ; I, IT, III. first. second, 
and third pairs of abdominal dilated trachez, forming a plexus behind the ovaries: 
1, pair of enormous thoracic air-sacs ; 2, pair of smaller air-sacs ; 3-7. abdominal 
air-sacs ; oc, ocular dilated trachea and air-sacs; c, cephalie trachea. The relations 
of the heart. to tne dorsal trachee are indicated.—Drawn by Emerton from dissec- 
tions by author. 
