Prof. G. J. Allman on the Anatomy of Acton. 153 
five lines in diameter, and I at once recognised it as similar to 
what I had observed in considerable abundance upon the leaves of 
Zostera marina in the locality where the Acteon was captured. 
It consisted of numerous ova enveloped in a gelatinous covering, 
and deposited in the form of a ribbon rolled into a plane spiral. 
In about six days after the deposition of the spawn the eggs were 
hatched, and the young Actzeons, Pl. VII. figs. 10, 11, 12, escaped, 
not in any respect resembling the parent, but of a totally different 
type of organization,—very similar to what has of late years been 
observed in the young of Doris, Aplysia, and some other Gaste- 
ropoda. 
The embryo-Acton is inclosed in a nautiloid shell, and fur- 
nished anteriorly with two oval dises, figs. 10, 11 aa, ciliated along 
the margin, and capable of being appr oximated till the upper sur- 
faces are brought into contact, “fig. 11, and again separated till 
they lie nearly i in the same plane, fig. 12. The discs are con- 
tinued anteriorly into a sort of foot, figs. 10, 116, also ciliated 
on the margin and provided with an operculum, figs. 11, 12 c, 
which is drawn after the little animal when it retires into the re- 
cesses of its shell, and thus completely protects it from all intru- 
sion from without, fig. 12. 
Near the place where the foot joins the discs are two ocelli- 
form spots, figs. 10, 11, 12 d, doubtless visual organs, though Van 
Beneden considers what are evidently the same organs in the 
embryo of Aplysia, as the rudimental cesophageal ganglia. That 
the organs under consideration are not ganglia, would alone ap- 
pear from their high refractive power. 
I could not succeed in detecting a mouth, though a tube, 
fig. 11 e, which I believe to be an cesophagus, may with some care 
be traced from the root of the discs backwards, till it dilates into 
an oval cavity or stomach, f, part of which is concealed beneath a 
granular mass, g, which occupies the posterior convolutions of the 
shell. 
Near the origin of the cesophagus are two spherical bodies, / ; 
these I believe to be the true rudiments of cesophageal ganglia. 
Two fibres, fig. 11 72, may be seen to run from the root of the 
dises backwards, and would seem to have some attachment to the 
interior of the shell ; they bifurcate near their termination. It is 
difficult to say whether they be nervous filaments connected with 
the cesophageal ganglia, or muscular fibres destined for the re- 
traction of the embryo. 
The little embryo is eminently natatory, swimming about with 
wonderful activity by means of its curious ciliated discs, and by 
its varied and elegant gyrations, constituting an object of great 
beauty and interest. 
