SILK SPINNING. 453 



with very tiny black dots. It is an exceedingly variable 

 insect, and there is one variety which now and then occurs in 

 which the brown bands are absent and the whole of the wings 

 is covered with the little black dots. There is no difficulty 

 in distinguishing the female from the male, as may be seen 

 by referring to Fig. b in the same Woodcut. The wings 

 are reduced to the merest rudiments, and are not only useless 

 for flight, but absolutely useless for any purpose whatever. 

 Like those of the ostrich and emeu, they are inefficient as 

 wings. But the two birds which have been mentioned are^ 

 exceedingly swift of foot, and the wings, though they are 

 not used for flight, do at least assist them in running. But 

 the female Mottled Umber is by no means swift of foot, and 

 indeed a distance of six inches is quite a journey to her. The 

 body of the female is warm brown in colour, and on each seg- 

 ment are two conspicuous black spots. This larva is shown at 

 Fig. c in the same Woodcut. 



The larva is one of those which are furnished with a spinning 

 apparatus, and use it for defensive purposes. 



I may here remark that, in all silk-spinning caterpillars, the 

 machinery is the same, though the length, quantity, and 

 quality of the silk differ greatly. Along each side of the body, 

 and closely pressed against the digestive organs, grows the 

 silk- vessel. This is a tube of greater or less capacity according 

 to the needs of the insect, in which is secreted the peculiar 

 substance which is known as silk. Each of these tubes ends in 

 a very slender outlet, scarcely as thick as a human hair, and 

 the two outlets unite in an instrument which very much 

 resembles the barrels of a double-barrelled pistol. Through 

 ^hese tubes or barrels the gummy secretion is forced, and 

 hardens as soon as it comes in contact with the atmosphere. 



Those larvae in which the supply of this secretion is small 

 are very chary of it, and only use it for the purpose of spin- 

 ning the cocoon or hammock in which the caterpillar changes to 

 the pupal and perfect states. Those, however, in which the 

 supply is more abundant employ it in various ways, and are 

 often indebted to it for their escape from many foes. What- 

 ever they may be doing, or wherever they may move, they 

 always draw with tliem their silken thread, one end of which is 

 attached to the leaf or branch on which they are walking, so 



