7 
138 Miscellaneous. 
singular peculiarity, inasmuch as the four primitive, parts of the vi- 
tellus do not each separate into two spheres, as is the case in other 
known animals, but that, on the contrary, the four new spheres, 
which are much smaller, are deposited upon the old ones. 
The embryo presents, from its first appearance, a kind of thick 
disc, intersected by a median sht which might be taken as analogous 
to the primitive line of vertebrated animals, if subsequent observa-~ 
tions did not show that it is at the spot which this slit occupies that 
the mouth is formed. The embryo is composed, some hours after 
the appearance of this. slit, of two lateral wheels furnished with 
large.vibratile cilia, of a beak-like prominence, which afterwards be- 
comes the foot, and of a posterior rounded part in which the intes- 
tines are formed. | | 
Of all the internal organs, the ear is first developed; in a subject 
now under observation the ears are very visible, whilst the eyes are 
not yet formed. 
' After the organs of hearing, the shell is formed; I have heen iis 
to trace all the phases of its development, as well as of the opercu- 
lum which clothes the posterior surface of the foot... I now observe 
that the tail is on the point of detaching itself from the animal ; all 
the loops which retained it have disappeared, and the membrane, 
which clothed it internally, envelopes the viscera tightly, jeoxing-® a 
large space between them and the shell. 
The digestive apparatus, which is formed after the shell, is com- 
posed of a semicircular mouth, situated between the wheels at the 
base of the foot, of an elongated cesophagus, which terminates in a 
large stomachal pouch, and of an intestine curved in the form of a 
hook, which terminates in an anus situated on the right. The liver 
is entirely separated from the intestine on its first appearance ; it 
communicates afterwards with the stomachal pouch by a large aper- 
ture. 
The stomachal pouch, in which I have often seen infusoria, espe- 
cially Navicule, appears to be’ transformed into a buccal: mass, I 
have seen, in the embryos of another species of Nudibranchie, and 
which greatly resemble the embryos of Acton, that a protuberance 
furnished with projections in the form of spines was developed in the 
inside of this pouch. Probably this organ was the first vestige of the 
tongue. 
Now, nearly thirty days after the laying of the eggs, my embryos 
swim freely in water by means of their large lateral wheels. It is 
remarkable that these agile animals, which for nearly a fortnight are 
nourished on infusoria, have yet no trace of circulation. The heart 
does not yet exist, and it is impossible that I should have overlooked 
it. This fact interests me greatly ; and as I have seen the heart in 
embryos of other mollusks which were much more advanced in their 
development, there could be no possible error on this point. 
I hope to be able to continue the researches of which I have given 
avery incomplete sketch, by bringing some living embryos, or rather 
larve of Acteon, to Paris. I intend to follow their development. du- 
ring the winter, in order to ascertain the changes which must still 
