66 HOUSE, GARDEN, AND FIELD 



open, we find inside the shell a headless animal with six 

 pairs of legs, each ending in two lashes, which are jointed 

 and fringed like those of a rock-barnacle. Unlike as they 

 are on superficial examination, the two kinds of barnacle 

 are evidently closely allied, and we do well to give them 

 a common name. But they must be distinguished from 

 one another, and the names of stalked and sessile barnacles 

 are in common use. The sessile barnacle is what we have 

 hitherto called the rock-barnacle ; it is also called the 

 acorn barnacle. 



To what division of animals do the barnacles belong ? 

 Any young student of the twentieth century, who had 

 received a few lessons in systematic zoology, would reply 

 at once that having jointed limbs they must be referred 

 to the Arthropods, and further that their aquatic habitat 

 places them in that division of Arthropods which is known 

 as the class Crustacea. Our young student, relying on the 

 definitions of the books, would be quite right, little credit 

 to him ! Other naturalists have cleared the way, and his 

 task is no harder than that of looking out words in a 

 dictionary. But before good textbooks or definitions 

 existed it was not easy to say where the barnacles ought 

 to be placed. Linnaeus put them among the mollusks, 

 and many years later the great Cuvier, who by his own 

 labours had greatly extended the knowledge of mollusks 

 as of many other groups of animals, made the same mis- 

 take. Barnacles, he said, have external calcareous shells, 

 like bivalve mollusks, and the body is not segmented as in 

 crustaceans. It is true, he goes on to say, that the 

 barnacles have jointed limbs, very like those of crustaceans, 

 a mouth provided with lateral jaws, and a chain of nervous 

 ganglia, but the Teredo or shipworm, which is certainly a 

 bivalve mollusk, has jointed limbs too (this is a strange 

 mistake of Cuvier's). On the whole he decided to leave 

 the barnacles among the mollusks, acknowledging at the 

 same time that they lead up to the crustaceans, and not 

 at all blaming those who rank them as such. Cuvier's 



