80 SEA-SHORE LIFE 



The esTss of criistaceaas are often carried about attached to the 

 abdominal appendages of the female. In the lower forms the egg 

 usually develops into a more or less oval-shaped emljr^'o called a 

 uaupliHs, which has a single eye and three pairs of appendages. 

 The first pair is simple and becomes the front feelers of the adult, 

 while the other two pairs are forked, and become the second pair of 

 feelers and the mandibles. In the higher crustaceans the eggs often 

 contain so mvicli yolk that the embryo is not set free until its devel- 

 opment has gone farther than the nauplius stage. Good general 

 descriptions of our Crustacea are given in Arnold's "Sea Beach at 

 Ebb-Tide;" Stebbing's "Crustacea," in The International Scientific 

 Series, 1893; and Volume II of "The Riverside Natural History," 

 edited by Kingsley. 



THE BARNACLES 



The older naturalists believed that barnacles were mollusks, but 

 a study of their development showed that they are crustaceans re- 

 lated to the water fleas. 



The egg of the barnacle is set free in the water and develops 

 into a minute larva Avith a triangular shield over the back, a single 

 eye immediately above the brain, a mouth, intestine and three pairs 

 of appendages. The larva then moults a number of times, acquir- 

 ing a pair of stalked eyes, and a pair of shells hinged along the back 

 and projecting over the sides of the body. The first pair of append- 

 ages have now changed into organs of attachment which enable 

 the little creature to fasten itself head-on to some rock or other sviit- 

 able anchorage where it is destined to pass the remainder of its life. 



A considerable change then comes over the creature. It re- 

 mains without food while it develops a shell with hinged lids which 

 may close or open the aperture. The barnacle has been described 

 as a crustacean which is fastened by its head, lies on its back, and 

 kicks its food into its mouth. If one watches a barnacle one will 

 see how the feathery jointed legs are thrust out at regular intervals, 

 and wave gracefully through the water to aerate the blood, and to 

 set up currents which drive small creatures into the mouth of the 

 barnacle. 



Most of the barnacles are hermaphrodites, but in some genera 



