INTRODUCTION. 2 



"known that the sense of smell is far more highly developed 

 in most animals than it is in man. It is certainly not very 

 marvellous that young animals should follow the scent of an 

 element in which their parents and ancestors have lived for 

 unknown ages. This is yet more plainly seen in the far- 

 famed instinct of metamorphosed insects, which always lay 

 their eggs on places suitable for the nourishment of the 

 escaping caterpillars, without recognising these places abso- 

 lutely by their own sight. Here, without doubt, they are 

 guided in their action by the sense of smell, so highly 

 developed in insects, and perhaps also by some kind of 

 memory from their caterpillar or maggot condition. "The 

 Sphinx Euphorbia" says Noll, (p. 15,) "knows the milk- 

 wort by its shape more than by its smell. And why should 

 it not? Is it not the particular flower with which it is 

 thoroughly acquainted? Has it not itself in its growth, in its 

 caterpillar stage, lived always on this plant, imitated its 

 color, and nourished itself on this alone ? Has it not built 

 up its body out of its tissue, taken into itself its volatile 

 oils and its alkaloids? Do we not note how the land- 

 fly, which kills the caterpillar of the swallow-tail butterfly, 

 Papilio machaon, by stinging it behind the head, spreads a 

 strong smell over the carrots on which it lives ? It is also 

 known that the blood of many insects, and especially of 

 larvae, smells of the plants on which they feed. The 

 dancing butterfly, seeking honey as its food, certainly knows 

 what it enjoyed in its youth and where it lived ; for even 

 though its form be changed, though its intestines with their 

 peripheral nerves have disappeared with its transformation^ 

 yet the chief part of its central nervous system remains, as 

 has been proved in the transformation of caged insects, and 

 may therefore, have well preserved the youthful impressions, 

 which in man are indeed the most lasting." So the moth 

 finds its way into locked-up cupboards of clothes, which it 

 has never seen, merely by the aid of smell, and when we, as 

 a protection against it, put strong-smelling substances, such 

 as camphor, turpentine, etc., among the clothes, we do so to 

 conceal the smell of the woolstuffs by a stronger smell, and 

 so to deceive the scent of the moth. Of what great and 

 marvellous performances the smell of insects is capable is 

 proved by the well-known fact, that if, in the midst of an 

 inhabited place, we expose a female moth in the window, the 



