THE C IRRIPEDIA . 
475 
species, with a short flattened peduncle, with calcareous scales), 
and depressed. The larva has a shell in the form of a carapace, 
which is cut short or truncated in front, where it has a horn on 
each side. The under surface of the larva is flat and broad, and 
is formed of thinner membrane than the back or dorsal surface- 
The horns just alluded to are long in the larva of Lepas anatifera , 
and short in the species Scalpellum , now being described, and 
their ends are either rounded and excessively transparent, or 
furnished in other kinds with an abrupt minute sharp point. 
larva OF Scalpellum vulgarc (from below.) larva, second stage. (After Darwin.) 
Mr. Darwin saw distinctly a long thread-shaped organ bear- 
ing excessively fine hairs in lines so exactly like the long plumose 
spines on the antennae of the larva of the last stage (and by 
which the mature Balanus adheres to surfaces) that he had not 
the least doubt that these horns were the cores in which antennae 
were in process of formation. Behind these horns, and near each 
other on the lower surface (sternal) of the body, there are two 
other minute doubly curved horns, and within each of them 
there is a most delicate and jointed thread-shaped structure on 
a thicker base. There are thus at first two sets of antennae in 
the larva. Anterior to the points of origin of the smaller antennae 
is seated a heart-shaped eye, but in some species this eye is not 
perfectly developed when they are born. There are three pairs of 
limbs seated close together ; each leg of the first pair always con- 
