PARASITES OP ANIMALS. 



Fig. 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. 



FiGUUE 1 . — " Hundred-legs," ( Scolopocrt/ptops sexspinosa Say), natural size; color 

 deep orange, with yellow feet. From Packard's Guide. 



Figure 2. — Nervous system of Corydalus eomutas, a large neuropterous insect; 

 a and b, ganglions of the head; c, the three ganglions of the thorax, which send 

 nerves to the three pairs of legs ; d, d, the eight double ganglions of the abdomen. 

 From Packard's Guide, after Leidy. 



Figure 3. — ^Portion of one of the tracheae or breathing tubes, prepared so as 

 to show the spiral fibre a, a part of which has been unwound; c, a secondary 

 branch. From Packard's Guide. 



Figure 4. — Transverse section of the thorax of a bee; a, one of the nervous 

 ganglions ; b, breathing pore or spiracle, opening into the tracheae, 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. 



