430 SUPPLEMENT 
in anatifse, are placed at certain periods in the folds of the 
mantle. The latter is formed of an extremely thin membrane, 
which lines the interior of the shell, and in which wind in- 
numerable vessels. 'Two appendages of this membrane, 
placed on each side of the animal, in which is remarked a 
wide canal, filled with a lacteal humour, which ramifies into 
a body fringed with a purple colour, form, according to Poli, 
the gills of the balani. We have some difficulty in believing 
that they differ so much from those of anatifee, which we have 
just described after the Baron Cuvier. Four teeth arranged 
in pairs, one above the other, and surrounded by an equal 
number of crustaceous palpi, bristling with sete, arm the 
mouth externally. The intestinal canal makes the circum- 
ference of the body, reascends behind towards the base of the 
proboscis, and terminates in this place, by an oval aperture, at 
the bottom of which the heart may be seen to beat. It is also 
towards the proboscis that we discover the small end of the 
testicles, which are two claviform sacs placed on each side of 
the body. They are continued with a canal which winds into 
the proboscis, which Poli has observed filled with a whitish 
and opake fluid, similar to that contained in the testicles, and 
from which the same fluid trickled, when he compressed the 
latter. The same author thinks that the fecundation of the 
eggs takes place out of the body, by means of the proboscis, 
which inclines downwards, to shed on them the spermatic 
fluid. 
The shell of the balani has, in the majority of species, an 
oval or rounded form, which gives it some resemblance to an 
acorn. From thence the generic denomination under which 
they are described. Six valves, which touch each other by 
their base, and separate towards their summit, essentially 
compose this shell. But a single species is known in which 
there are but three valves. The interval which they leave 
between these and their summit, is filled with testaceous 
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