42 THE INDUSTRIES OF ANIMALS. 



he preys ; he therefore punctures the petals of these 

 flowers in order to promote the exudation of this 

 viscid secretion. 



Many of us in our schooldays have admired the 

 intelligence of Jackdaws having their nests in some 

 old tower or belfry. They are able to distinguish 

 according to the hour the significance of the various 

 school bells. Most of these clangs do not move them, 

 and they continue to attend to their affairs without 

 paying attention. Their attention is only attracted 

 by the ringing which marks the beginning and the end 

 of recreation time. At the sound of the first they all 

 flee and abandon the courts before even a single pupil 

 has yet appeared. The bell, on the contrary, which 

 marks the end of recreation time invites them to 

 descend in a band to collect the crumbs of lunch. 

 They arrive in a hurry, so as to be the first to profit 

 by the repast, not waiting even until the place is 

 abandoned ; they know very well that the young 

 people still there are not to be feared, having no time 

 now to be occupied with them. 



In this class of facts, there are a certain number 

 which may be considered as more marked by custom 

 and perhaps less marked by spontaneous reflection. 

 Such, for example, is the custom of Sharks and Sea- 

 gulls to follow ships. 



In the seas where Dog-fish are abundant, one or 

 more of them become attached to a ship, and quit it 

 neither night nor day. One may believe sometimes 

 that they are not there ; but if any object is thrown 

 into the sea, the fin of one of these monsters appears 

 at the surface ; everything which is thrown overboard 

 disappears in their large jaws — kitchen refuse, bottles, 

 etc. When a dead body is thrown into the sea it 



