308 INSECT ARCHITECTURE. 



neither Lyonnet nor Cuvier could detect any vessel 

 issuing from it ; and consequently the fluid which is 

 analogous to blood has no circulation. It differs also 

 from the higher orders of animals in having no 

 brain, the nerves running along the body being only 

 united by little knobs, called ganglions.* Another 

 circumstance is, that it has no lungs, and does not 

 breathe by the mouth, but by air-holes, or spiracles, 

 eighteen in number, situated along the sides, in the 

 middle of the rings, as may be seen in the following 

 figure from Lyonnet : 



Caterpillar of the Goat-Moth (Cossus ligniperda). 

 These spiracles communicate on each side with 

 tubes that have been called the wind-pipes (trachece).\ 

 The spinning apparatus is placed near the mouth, 

 and is connected with the silk-bags, which are long, 

 slender, floating vessels containing a liquid gum. 

 The bags are closed at their lower extremity, become 

 wider towards the middle, and more slender towards 

 the head, where they unite to form the spinning-tube, 

 or spinneret. The bags being in most cases longer 

 than the body of the caterpillar, necessarily lie in a 

 convoluted state, like the intestines of quadrupeds. 

 The capacity, or rather the length of the silk-bags, 

 is in proportion to the quantity of silk required for 

 spinning; the Cossus ligniperda, for example, from 

 living in the wood of trees, spins little, having a bag 

 only one-fourth the length of that of the silk-worm, 

 though the caterpillar is at least twice the dimensions 

 of the latter. The following figure, taken from the 



* See Insect Transformations, concluding chapter, 

 t Ibid p. 155. 



