THE LAEVA 27 



have thought that it sought out its food by some sense other than 

 that of vision. 



Another important and interesting feature of the head is the 

 silk-spinning apparatus, situated under cover of the lower lip. This 

 consists of two tubular glands, corresponding to our own salivary 

 glands, the special purpose of which is to secrete a viscid fluid that 

 solidifies on exposure to air. The opening by which the fluid 

 escapes is so situated that the caterpillar can easily apply it to the 

 surface of any object over which it is walking, and then, by draw- 

 ing or turning away its head, cause a silken fibre to be produced. 



Some caterpillars make use of this spinning apparatus only on 

 a few special occasions, but others, more especially some of the 

 smaller species, seem to have it always in use, so that if at any 

 time you suddenly start them into the air by giving a smart tap to 

 the plant or twig on which they rest, they invariably fall slowly 011 

 the end of a growing web, the spinning of which they stop as soon 

 as they consider they have fallen far enough. Sometimes, as you 

 are walking through a w r ood, you will see hundreds, nay, thou- 

 sands of little caterpillars thus suspended, swinging gently in the 

 breeze. Not long since, after only a few minutes' walk among the 

 trees of Epping Forest, I found I was decorated with several dozens 

 of these swingers with which I had come into collision in this 

 case consisting chiefly of the larvae of the Green Tortrix Moth 

 (Tortrix viridana). 



Now let us examine the caterpillar's limbs. Attached to each 

 of the second, third, and fourth segments is a pair of true walking 

 legs, corresponding with those of the perfect insect. TJiese are 

 covered with a hard and shining substance, and are also each 

 provided with a hook. The fifth and sixth segments have no limbs 

 at all, nor have the eleventh and twelfth, but some or all of the 

 others (seventh, eighth, ninth, tenth, and thirteenth) are furnished 

 with a pair of claspers which we shall presently describe. 



First, as regards the number of claspers, it will be seen from 

 what has just been said that this is not always the same. Some 

 caterpillars possess five pairs, thus making up the total number of 

 walking appendages to sixteen. In fact, we must regard this as the 

 usual number. But there are at least a few hundred exceptions to 

 the rule. Many of the Bombyces (page 217), for example, have only 

 four pairs of claspers ; and in others of the same group the fifth 

 pair is present, but only partially developed, and quite useless for 

 walking. 



