SPINNIXG CATERPILLARS. 269 



spiracles, eighteen in number, situated along the sides, in 

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

 figure from Lyonnet. 



w / 1^ 

 ("aterijillar of the Goat Moth (iCossus Uaniperda). 



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 con- 

 nected 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, neces- 

 sarily 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 ligniperdciy 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 admirable treatise of 

 Lyonnet on the anatomy of the Cossns, will render these 

 several organs more easily understood than any descrip- 

 tion. 



The spinneret itself was supposed by Eeaumur to have 

 two outlets for the silk ; but Lyonnet, upon minute dissec- 

 tion, found that the two tubes united into one before their 

 termination ; and he also almost assured himself that it was 

 composed of alternate slips of horny and membranaceous 

 substance, — the one for pressing the thread into a small 

 diameter, and the other for enlarging it at the insect's 

 pleasure. It is cut at the end somewhat like a writing- 

 pen, though with less of a slope, and is admirably fitted 



