HALF AN HOUR WITH CRUSTACEA. 229 



a similar relationship? In some respects, to the 

 eye these animals seem real molluscs, or shell-fish, 

 the latter kind especially. You examine one and find 

 that the stalk is a muscular tube, to the summit 

 of which two or more large shells, not unlike the 

 valves of Tellina, enclose long, feathery tentacles. 

 The shells are tinted light blue, and, when detached, 

 have much of the look of ordinary bivalves. Or, 

 bestow a moment's extra attention on the common 

 acorn-shells (Balanus) which encrust the stones, 

 rocks, and larger bivalve mollusca. They well 

 deserve their popular name, for, in outward shape, 

 the entire structure is not unlike the upper half of 

 an acorn. These, you see, have no stalk, but are 

 attached to their places by the base of the shell, so 

 as to be called " sessile." Like the true barnacle, 

 each individual domicile is composed of several parts, 

 hence the name of " multivalve " was given to them 

 when they were regarded as mollusca. There is 

 one barnacle (Scalpellum vulgare) which has the 

 valve nearly oval. When these open, a hand of 

 bristly tentacles is hastily thrust forth, and as 

 suddenly drawn in again. This species is small, 

 and not unfrequently is found attached to the bases 

 of a cluster of Corallines. The larger species, and 

 that which we have mentioned as clustering on old 

 wrecks, &c., is the Lepas anatifera, about which the 

 tale was formerly told, and firmly believed in, that 

 they were descended from a species of goose, and 

 that, in turn, they brought forth geese ! We have 



