A452 Miscellaneous. 
strongly magnified, numerous colourless nuclei are detected ; lastly, 
the mantle becomes covered with small tubercles furnished with 
vibratile cilia. By means of these cilia and of the ciliary coat of the 
vitelline vesicle, the embryo executes continual movements of rota- 
tion, which persist until the end of its embryonic development. 
In its anterior part the vitellus of nutrition presents a projection 
corresponding to the mantle; it also gives off two prolongations into 
the cephalic sinuses beneath the optic ganglia. The author denies 
that this vitellus is surrounded by the proper membrane described 
by M. Kolliker. 
Third period.—During this period the apparition of new organs 
plays quite a secondary part. The essential phenomenon is the de- 
velopment and change of proportions of the organs already existing 
in a rudimentary state. In fact we have hardly anything to indicate 
except the appearance of the fourth pair of arms towards the com- 
mencement of the second half of this period, and that of the fifth 
pair towards its end. The vitellus of nutrition passes by little and 
little into the body of the foetus, and finally only represents a sort of 
wart upon the head between the bases of the arms. This external 
vitellus communicates with that of the interior of the body by a 
delicate band which passes through a small orifice situated below 
the mouth. At the moment of exclusion, this last vestige of the 
external vitellus passes entirely into the interior of the body. 
In this last period occurs the organization of the skin, formed at 
first of two layers of cells, one representing the dermis, the other 
the epidermis. In the former the chromatophora soon make their 
appearance ; they are at first immobile, but afterwards change their 
form under the influence of muscular fibres, which are developed 
about the middle of this period. It is also at this epoch that we 
witness the first appearance of small very refractive granules, which, 
by their union, will subsequently form the dorsal bone. During 
this third period the cartilages are formed at the expense of the 
inner blastodermic lamella. The ocular cartilages are the first 
formed. This is also the period of the formation of the sucking- 
disks on the arms. The nervous system becomes more differentiated, 
and the stellate ganglia appear. 
On the first day of the third period, the envelope of the eye 
divides into two laminee, the outer of which alone presents a cen- 
tral orifice. The crystalline has at first the form of a small rod 
attached to the rudiments of the ciliary body. It is a homo- 
geneous body, originating by the hardening of the secretions of 
the ciliary body (as has already been shown by M. Hensen). To- 
wards the end of this period a kind of cornea is formed; at the 
same time we see a great number of very fine fibres, producing 
the characteristic phenomena of interference, make their appearance 
in the silvery coat. The author refutes the opinion of M. Kolliker, 
according to which the organs of hearing make their appearance in 
the form of compact and solid bodies. He asserts that in the Sepiole. 
the formation of these organs presents a complete parallelism with 
what we know of their development in the Vertebrata. As to the 
