Animals Before Man 



even were perhaps not developed, and protect- 

 ive mimicry probably played but small part* 

 in the struggle for existence ; the law of the 

 world was might, and the weaker went to the 

 wall. 



As the smaller fishes of the Devonian period 

 died out, sharks and their relatives, which first 



The sleeper shark, Somniosrts microcephalus, a large but harm- 

 less species. 



appeared in Silurian times, came upon the scene 

 in numbers ; not sharks as we now know them, 

 but smaller and simpler forms, which were 

 later on replaced by others more like those of 

 to-day. We are very apt to think of sharks as 

 great and formidable monsters ready to tear 



* It is perhaps hardly necessary to warn the reader that this 

 is pure theory, although it has much of probability back of it, for 

 protective resemblances could hardly have originated by any other 

 process than that of a slow weeding out of the more conspicuous 

 individuals. 



104 



