DARWIN. 227 



in fact I considered the task an impossibility ; but 

 at a rough calculation, I concluded there would not 

 be less than a million. Dr. Darwin, however, 

 travelling in the Falkland Isles, met with a riband 

 of spawn from a white Doris (the animal itself was 

 three and a half inches long), which measured twenty 

 inches in length, and half an inch in breadth ! and 

 by counting how many balls were contained' in a 

 tenth of an inch in the row, and how many rows in 

 an equal length of riband, this gentleman reckoned 

 that upon a moderate computation there could not 

 be less than six millions of eggs. Yet, in spite of 

 such amazing fecundity, this Doris was not common. 

 ' Although/ says Dr. Darwin, ' I was searching under 

 the stones, I saw only seven individuals. No fallacy 

 is more common with naturalists, than that the 

 numbers of an individual species depend on its 

 powers of propagation.' 



This apparent paradox is not difficult of explana- 

 tion when we consider the number of enemies which 

 are always hovering near, and ready with hungry 

 mouths to snap up the infant embryos as soon as 

 they begin to show signs of vitality. The Hermit- 

 Crabs are especially fond of Doris spawn, so much 

 so, indeed, that the writer could never retain any 

 for hatching purposes while any of the Paguri were 

 near. Mr. Peach says they (the young Dorides) 

 have myriads of enemies in the small Infusoria, 

 which may be noticed, with a powerful microscope, 



