THE TIGER MOTH. 



645 



vessels in the interior, which contain a gelatinous kind of substance, 

 and become enormously large just before the caterpillar is about to 

 change into a pupa. Both the silk organs unite in a common tube at 

 the mouth, technically called the spinneret, and through this tube the 

 semi-liquid is ejected. As soon as it comes into contact with air it hard- 

 ens into that soft, shining fibre with which we are so familiar. 



If a single fibre of silk be examined through a good microscope, it 

 will be seen to consist of two smaller fibres laid parallel to each other, 

 like the barrels of a double gun, this structure being due to the double 

 secreting vessels. The goodness of silk consists chiefly in the manner 

 in which these semi-fibres are placed together. 



The caterpillar employs the silk for the purpose of constructing a 

 cocoon in which it can lie until it has assumed the perfect form, and 

 proceeds with won- 

 derful regularity 

 and despatch in 

 its work, its head 

 passing from side 

 to side, always 

 carrying with it a 

 thread, and the 

 cocoon being grad- 

 ually formed into 

 the oval shape 

 which it finally 

 assumes. The few outermost layers are always rough and of poor qual- 

 ity ; these are stripped ofi", and, the end of the thread being found, it is 

 fastened to a wheel and spun oflT into a hank of soft yellow fibre. The 

 coloring matter is very variable, being sometimes hardly visible, and at 

 others giving the silk a bright orange tint. It fades much on exposure 

 to light. 



The family of the Arctiidse — so called because some of the hair-cov- 

 ered larvae have a bear-like look — is represented in England by many 

 examples, some being really handsome insects, and others remarkable 

 for some peculiarity in themselves or the larvse. 



The Tiger Moth. — This common but beautiful moth is found in 

 the beginning of autumn. It runs on the ground with such swiftness 

 as often to be mistaken for a mouse. I have more than once seen a 

 kitten chasing a Tiger Moth among the flowers in a garden, evidently 

 deceived by its resemblance to a mouse. The larva is popularly called 

 " the woolly bear." It is rather large, and is surrounded with tufts 

 of long elastic hairs of a reddish brown color, which serve as a defence 

 against many enemies. When disturbed it rolls itself round, just as 

 a hedgehog does, and if on a branch suffers itself to fall to the ground, 



The Wood Leopard Moth {Zeuzera cesculi). 



