166 



BOYS AND GIRLS IN BIOLOGY. 



about by the sinking and swelling of a vessel which runs 

 along the upper or dorsal side of the body. The blood 

 is a colorless, watery fluid, and you can see it flowing 

 into the dorsal vessel through little mouths in the sides. 

 Each mouth has a little valve, which * prevents the 

 blood from going back again. You may see this ves- 

 sel beating along the caterpillar's back, and the blood 

 is sent from the tail to the head, instead, as one would 

 suppose, from the head to the tail ; and this blood goes 

 back again by vessels on the under or ventral side. 



The caterpillar does not look or act like a nervous 

 individual ; nevertheless, he has a great many nerves. 

 You can see the chain of nerve-bunches, or ganglia, 

 running close to the digestive organs, connected by 

 cords, like the lobster's (Fig. 136). The bunches 

 above the gullet are the head ganglia, or the Brain^ 

 and they give off nerves to the eyes and other parts of 

 the head. The caterpillar's brain is not of so much im- 

 portance to it, for he has large bunches of nerve-matter, 

 ganglia, in other parts of his body. Besides, he does 

 not breathe through his mouth. If his head is cut off, 

 the part he misses most is the jaws ; and I suppose, if a 

 new pair would grow, he could get on about as well 

 without a head as with one. The most merciful way 

 to kill a caterpillar is not to cut off his head, but to stop 

 up his breathing-holes, and this can be done by smear- 



