BARNACLES. 255 



peda on emerging from the egg are quite free, and very 

 different from their parents. "They possess locomo- 

 tive organs, consisting of a large anterior pair of limbs, 

 provided with a sucker, and hooks for the purpose of 

 mooring themselves at pleasure to various objects and 

 also of six pairs of swimming-limbs, acting in concert like 

 oars. Besides these, they have a tail bent under the body, 

 consisting of two joints and terminating in four bristles : 

 this is an additional locomotive organ. Thus endowed, 

 they swim along in a series of bounds, the oars and tail 

 giving in measured time successive impulses. They have, 

 moreover, large lateral eyes set on peduncles, and the body 

 is covered with a sort of shell, as in certain Crustacea (e.g. 

 Cyclops), which they closely resemble," and for which Mr. 

 Thompson at first mistook them. 



In due time a metamorphosis takes place ; the shell is 

 thrown off, the eyes disappear, the limbs become trans- 

 formed to cirrhi, the regular valves develop themselves, 

 the peduncle shoots forth, and the animal becomes per- 

 manently fixed. 



Believing these little creatures to be the larvae of some 

 crustaceous animal, some of them, says Mr. Thompson, 

 were collected in the spring, and in order to see what 

 changes they might undergo, were kept in a glass 

 vessel, covered by such a depth of sea-water, that they 

 could be examined at any time by means of a common 

 magnifying-glass. They were taken May ist, and on the 

 night of the 8th the author had the satisfaction to find 



