Prof. G. J. Allman on the Anatomy 0/ Actseon. 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 Actceon 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 Actseons, PI. 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 DoriSy Aplysia, and some other Gaste- 

 ropoda. 



The embYjo-Actceon is inclosed in a nautiloid shell, and fur- 

 nished anteriorly with two oval discs, figs. 10, 1 1 ««, ciliated along 

 the margin, and capable of being approximated till the upper sur- 

 faces are brought into contact, fig. 11, and again separated till 

 they lie nearly in the same plane, fig. 12. The discs are con- 

 tinued anteriorly into a sort of foot, figs. 10, lib, 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 dj doubtless visual organs, though Van 

 Beneden considers what are evidently the same organs in the 

 embryo of Aplysia, as the rudimental oesophageal 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 oesophagus, may with some care 

 be traced from the root of the discs backwards, till it dilates into 

 an oval cavity or stomach, /, part of which is concealed beneath a 

 granular mass, ff, which occupies the posterior convolutions of the 

 shell. 



Near the origin of the oesophagus are two spherical bodies, h ; 

 these I believe to be the true rudiments of oesophageal ganglia. 



Two fibres, fig. lie i, may be seen to run from the root of the 

 discs 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 oesophageal 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. 



