88 



FIRST LESSONS IN ZOOLOGY. 



Crustaceans also occur everywhere under leaves and 

 stones in damp places; these are the " sowbugs." Some of 

 them, when disturbed, roll into a ball like a pill, hence 

 they are called "'pill-bugs/' Lastly, we come to the most 

 distant relations of the lobster. 



The barnacles would, at first glance, hardly be regarded 

 as Crustacea at all, so much modified is the body, owing to 

 their fixed, parasitic mode of life. The barnacle is (Fig. 

 94) a shell-like animal, the shell 

 composed of several pieces, with 

 a conical movable lid, having an 

 opening through which several 

 pairs of long, many-jointed, 

 hairy legs are thrust, thus cre- 

 ating a current which sets in 

 towards the mouth. The com- 

 mon barnacle abounds on every 

 rocky shore from extreme high- 

 water mark to deep water, and FIQ. 94. A Barnacle, 

 the student can, by putting a (Natural size.) 



group of them in sea-water, observe the opening and shut- 



FIG. 95. Young: of Baianus. 

 (Much enlarged.) 



FIG. 96. Pupa of a goose-barnacle, 

 Lepas. (Much enlarged.) 



ting of the valves and the movements of the slender hairy 

 legs. 



The metamorphosis of the barnacle is remarkable. After 

 leaving the egg, it swims about as a minute creature, rep- 



