The Structure and Special Physiology of Insects 19 
on it not merely to take up oxgyen from the outer air and give up the 
waste carbon dioxide of the 
body, but also to convey these 
gases to and from all the tis¬ 
sues of the body. The blood 
is not red, but pale yellowish 
or greenish, and is really more 
like the lymph of the ver¬ 
tebrate body than like its 
blood 
Insects do not breathe 
through the mouth or any 
openings on the head, but have 
a varying number (usually 
from two to ten pairs) of 
small paired openings on the 
Fig. 37. Fig. 38. sides of the thorax and abdo- 
FiGo 37.—Diagram showing respiratory system of pupa men. These Openings, called 
ol TpTracilsTre « ^des, or stigmata, are ar- 
enlarged.) ranged segmentally and in 
Fig 3 8 .—Oiagram of tracheae in head of cockroach. most j nsects are t0 be found 
Note branches to all mouth-parts, and the an¬ 
tennae. tracheae, or air-tubes. (After Miall on two of the thoracic seg- 
and Denny.) ments and on all the abdomi¬ 
nal segments except the last two or three. The openings are guarded by fine 
hairs or even little valvular lids to prevent 
the ingress of dust, and are the entrances to 
an extended system of delicate air-tubes or 
tracheae which branch and subdivide until 
the whole of the internal body is reached 
and ramified by fine capillary vessels bring¬ 
ing fresh air to all the tissues and carrying 
off the waste carbon dioxide made by the 
metabolism of these tissues. The usual 
general arrangement of this elaborate re¬ 
spiratory system is shown in Figs. 34, 35, 
and 36. Short broad trunks lead from 
each spiracle to a main longitudinal trunk 
on each side of the body, from which 
numerous branches arise, these going to 
particular regions of the body (Fig. 38) Fig. 39.—Piece of trachea (air-tube), 
and there branching repeatedly until ^ 
even individual cells get special tiny graph by George O. Mitchell.) 
