1877.] Barnacles. 107 
the animals either occur in groups, as in the genus Balanus, or 
the intromittent organ is extremely long, as in Acasta, thus en- 
abling one individual to fertilize another. Anelasma squalicola 
always occurs in pairs in the skin of sharks. 
But in the two genera, Jóla and Scalpellum, 
the individuals are either solitary or, if in clus- 
ters, are so crowded and twisted that the aper- 
tures of the capitulum are distant from each 
iT 
wR MINR 
Pannen tr 
other. Pmt 
: . ere ean 
The case of a simple separation of the sexes — japon 
would not strike us as being peculiar; but an 
instance where a hermaphrodite, with fully 
developed testes, vasa deferentia, and intro- 
mittent organ, besides female organs, has with- 
in its shell from one to ten complemental males 
can, I think, be explained only on the ground 
of adaptation for cross-fertilization. 
The eggs pass from the ovaries and are borne (Fre. 8) MALE OF 8. 
for some time inside the capitulum. They un- eskaerea 
dergo a total segmentation of the yolk and 
hatch a Nauplius, a free swimming form with mouth, stomach, 
and intestine, a triangular carapace with two prominent frontal 
horns and a posterior spine, beneath which is seen the forked ab- 
domen. (Figure 9, Nauplius of Balanus balanoides? from a 
MS. drawing by Dr. Packard.) They 
have three pairs of swimming feet, the 
first simple, the posterior two biramose, 
and all three terminating in long bristles. 
They soon change to a pupa form (Fig- 
ure 10, pupa of Lepas australis; a, an 
tennæ ; c, cirri; m, mouth; from Dar- 
win), which has the triangular shield of 
the Nauplius folded together in a bivalve 
T a cso form; the six pairs of thoracic limbs are 
resent, and also the antennæ. After 
swimming about for a while the ani- 
mal attaches itself by its antennæ, as 
shown in the figure, and undergoes a 
metamorphosis by which the eye be- 
comes internal, the antennæ are con- 
cealed by the growth of the peduncle, 
the valves of the capitulum are formed, 
and, in a word, the animal attains its adult retrograde condition. 
