294 TADPOLES OF THE SEA 



obtaining abundant nutriment and safety from enemies 

 has been, so to speak, " discovered " by a race of hitherto 

 active creatures is seen in many kinds of animals, and in 

 a more or less marked degree. The spiders, for instance, 

 are the descendants of scorpion-like ancestors, and as 

 compared with the many-jointed and variously endowed 

 scorpions are simplified. The spiders have a globular 

 unjointed body, very long, quickly-moving legs, and 

 deadly poisonous claws. They are " specialised " for 

 great strength and rapidity so as to catch insects and 



FIG. 40. Two individuals of the ship's barnacle (Lepas anatifera) 

 attached to a piece of wood. Usually they are seen hanging down- 

 wards from the substance to which they have fixed themselves. 

 Note the shell-like covering in the left-hand specimen, the pro- 

 truded legs (capable of being extended and suddenly withdrawn 

 into the shell), and the solid, leathery stalk which, as Fig. 41 shows, 

 was the creature's head. 



suck their blood. In them " simplification " is accom- 

 panied by great activity and by wonderful perfection of 

 the sense-organs and nervous system, resulting in their 

 marvellous powers of spinning threads and constructing 

 snares and nests. The spiders cannot be regarded as 

 inferior in special powers and endowments to the 

 scorpions ; indeed, they are far ahead of them. They are 



