M. Ussow’s Zoologico-Embryological Investigations. 221 
fifteenth day of development). ‘The upper germ-lamella forms 
only the. epidermis, composed of cylindrical, everywhere 
similar cells, covered in many places (especially on the mantle) 
in the rotating embryo with cilia. The outer, very thin layer 
of elongated cells of the dermo-muscular layer forms the so- 
called fibrous layer; whilst the chromatophores, and especially 
the fibres of muscular and connective tissue which lie in the 
cortum (cutis), are formed from the inner layers. The chro- 
matophores originate in the first half of the third period, from 
large round, at first nucleated cells of the dermo-muscular 
layer. The coloured protoplasm of these cells shrivels at the 
time when a very thick membrane appears upon the cell; by 
this means the nucleus becomes invisible. Such newly 
formed chromatophores, appearing first on the mantle and 
afterwards on the head and arms, begin to contract when the 
cells radiately arranged round them stretch into a spindle- 
shape, and thus form the contractile muscular fibres long 
since described by Keferstein * and Bohl f. 
I do not consider it necessary to describe here the formation 
of the cartilage in its details, as all that I have observed with 
respect to it in Sepia, Loligo, and Argonauta agrees perfectly 
with the results obtained by Metschnikoff {in the case of 
Sepiola. There is no doubt that all the cartilages differentiated 
in the third period (the cartilages of the cups, the eye-covers, the 
head, the fins, &c.) are developed from considerable thickenings 
(e. g. in the anterior cephalic lobe not far from the eyes) of the 
upper germ-lamella, at the spots where they are afterwards 
found in the adult animal. 
With regard to the development of the paired olfactory 
organ of the Cephalopoda, which lies on the ventral side 
behind the eyes and appears towards the end of the third 
period (Sepia, Loligo, Sepiola), originally in the form of a 
tubercle and then of a pit-like depression of the upper lamella, 
I can only confirm the observations of Kélliker §, Metsch- 
nikoff ||, and Tschernoff 4. 
With this I conclude the exposition of the results of my 
investigations of the development of the four above-mentioned 
species of Cephalopoda, which lasted uninterruptedly almost 
two years. At present engaged in extending and completing 
these studies, I hope soon to be able to publish a more 
detailed memoir. 
[To be continued. | 
* Bronn’s Klassen und Ordn. Bd. iii. Abth. ii. p. 1324. 
+ Beitr. zur vergl. Histol. p. 70, pl. iii. figs. 40 & 41. 
{ Loc. cit. pp. 39 et seq. § Loc. cit. pp. 107 et seq. 
|| Loe. cit. p. 53. 4] Bull. Soc. Imp. Nat. Mosc. 1869, p. 87, pl. i. 
