PARASITES OF ANIMALS. 3 
ment, which appear at first in the form of. 
little sacks containing fluid, but finally ex- 
pand into broad membranes and the sides 
of the sack unite so as to appear like a 
simple membrane, supported by little 
» branching, hollow rods, or tubes, which 
communicate with the cavity of the body, 
and also form the joints of the wings. The 
legs and jaws originate from the lower part 
of the sides of each ring that bears such 
appendages, so that there must be as many rings or segments 
in any part of the body as there are pairs of such organs, but 
Fig. 4. 
Freure'l.—* Hundred-legs,” (Scolopocryptops sexspinosa Say), natural size; color 
deep orange, with yellow feet. From Packard’s Guide.’ 
Ficure 2.—Nervous system of Corydalus cornutas, a large neuropterous insect; 
a and b, ganglions of the head; ¢, the three ganglions of the thorax, which send 
nerves to the three pairs of legs; d, d, the eight double Eanalions of the abdomen. 
From Packard's Guide, after Leidy. 
FicureE 3.—Portion of one of the trachez or breathing tubes, prepared so as 
to show the spiral fibre a, a part of which has been unwound; ¢, a secondary 
branch. From Packard’s Guide. 
Ficure 4.—Transverse section of the thorax of a bee; a, one of the nervous 
ganglions; 0, breathing pore or spiracle, opening into the trachez, which branch 
in the interior, and send small tubes into the legs and wings; c, the dorsal vessel 
or pulsating organ, which circulates the blood; d, the intestine. From Packard’s 
Guide. Digitized by Microsoft® 
