1^ 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 slit 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 been able 

 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, leaving 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 NaviculcB, appears to be transformed into a buccal mass. I 

 have seen, in the embryos of another species of Nudibranchise, and 

 which greatly resemble the embryos of ActiEon, 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 moUusks 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 

 a very incomplete sketch, by bringing some living embryos, or rather 

 larvae of Actaon, to Paris. I intend to follow their development du- 

 ring the winter, in order to ascertain the changes which must still 



