126 HUMBLE CREATURES. 



this greedy little plague is frequently drawn iato oiir 

 parlours by the sweets of our domestic establish- 

 ments ; but, looking at one or two of the analogous 

 examples in other creatures to which we have just 

 referred, we find the principle established beyond a 

 doubt. The Bee, for instance, rises up in a vertical 

 Hue in the air before it can ascertain in which direc- 

 tion to fly in search of flowers, and, guided by the 

 sense of sight, it then flies ofi' in the right direction ; 

 again, the dog seeks his master's "trail," and, di- 

 rected by the sense of smell, traces its owner. 



But, on the other hand, it must not be supposed 

 that we entirely disagree with the second theory, 

 that instincts are called into operation by certain 

 sensations, and no doubt practice or use renders the 

 senses acute, and often animates the latent instinct, 

 without any impulse from within. This state of 

 things is illustrated by the humorous saying often 

 applied to greedy children, that "when geese see 

 water they are thirsty;" and that the sense has such 

 great influence in the direction of the acts of the 

 insect as almost to make it appear the constant ex- 

 citing cause, is proved by the Mesh-fly depositing her 

 eggs on the flowers of Stapelia hirsuta, the smell of 

 which resembles carrion ; or the common House-fly 

 placing hers on snuff which is similar in odour to 

 dung ; neither substance, however (the flower nor the 

 snuff), being suitable for the nourishment of the 

 young brood. 



We can therefore agree with the first theory, that 



