158 THE ANIMAL KINGDOM. 



and the brain, are their food and abiding place. There is 

 scarcely one animal, especially of the vertebrate classes, 

 which is not infested by several species. The human body- 

 has eighteen internal parasites, and those which inhabit 

 one animal are rarely found in one of another genus. 

 Those who desire further knowledge of these parasites, had 

 better read ' Owen's Hunterian Lectures/ vols. iv, v, vi. 



