206 Marsh. 



Here is a strange caterpillar staring at us with its bright 

 red head drawn back into the swollen thorax, the whole 

 thrown back threateningly, thus giving it quite a formidable 

 aspect, whilst the tail, divided as it is into two fine fila- 

 ments, adds to this appearance. You need not be afraid of 

 it, dangerous as it looks. Touch it! Ah, from the under side 

 of the first thoracic segment, directly below its mouth, and 

 which is placed straight towards you now that its head is 

 raised, it squirts a fluid upon your hand. You draw back 

 quickly. A piece of blue litmus paper put into the fluid be- 

 comes red, from which we know that the fluid is acid. If I 

 had a little bicarbonate of soda here, I would put a pinch 

 into the drop of fluid, and effervescence would follow. The 

 acid is called " formic " acid because it was first obtained 

 from ants. You touch the caterpillar again on the opposite 

 side, and immediately the threatening head is brought round 

 to the fresh point of attack, and some more acid is squirted. 

 It is evidently by the sense of touch that the caterpillar is 

 guided as to the direction in which to squirt the fluid. Hav- 

 ing seen how well the caterpillar of the Puss moth can pro- 

 tect itself, let us now examine the glands from which the 

 fluid comes. Quite at the centre of the ventral surface of 

 the first thoracic segment, and placed transversely across it, 

 we find a narrow slit. By squeezing this, four little pro- 

 cesses are pressed out, two on each side, whilst between 

 these is a central gland in which the acid is secreted. Have 

 the caterpillars of other moths such an arrangement? Yes ; 

 some moths closely allied to the Puss, but smaller, and hence 

 popularly termed Kittens, have very similar glands ; but they 

 are unable to use them as the Puss moth does, and there is no 

 doubt that, although not so conspicuously useful, they sub- 



