56 THE EVOLUTIONIST AT LARGE. 



Here they could get little or no lime, and so 

 their shells grew smaller and smaller, in 

 proportion as their habits became more de- 

 cidedly terrestrial. But to the last, as long 

 as any shell at all remained, it generally 

 covered their hearts and other important 

 organs ; because it would there act as a spe- 

 cial protection, even after it had ceased to be 

 of any use for the defence of the animal's 

 body as a whole. Exactly in the same way 

 men specially protected their heads and 

 breasts with helmets and cuirasses, before 

 armour was used for the whole body, because 

 these were the places where a wound would 

 be most dangerous ; and they continued to 

 cover these vulnerable spots in the same man- 

 ner even when the use of armour had been 

 generally abandoned. My poor mutilated 

 slug, who is just now crawling off contentedly 

 enough towards the hedge, would have been 

 cut in two outright by my hoe had it not been 

 for that solid calcareous plate of his, which 

 saved his life as surely as any coat of mail. 



