M. Ussow's Zooloyico-Emhryological Investigations. 221 



fifteenth day of (levclopmeiit). The upper fferm-lameHa forms 

 only tlie epidermis^ composed of cylindrical, everywhere 

 similar cells, covered in many })laces (especially on the mantle) 

 in the rotating embryo Avith cilia. The outer, very thin layer 

 of elongated cells of the dcrmo-muscular layer forms the so- 

 called Jibroiis layer] whilst the cliromatopliores^ and especially 

 \\\(i Jibres of muscular and connective tissue wliich lie in the 

 carium {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 aiTanged round them stretch into a spindle- 

 shape, and thus form the contractile muscular fibres long 

 since described by Keferstcin * and Bohl f. 



I do not consider it necessary to describe here the formation 

 of the cartilage in its details, as all that 1 have observed with 

 respect to it in Sepia, Loligo, and Argonauta agrees perfectly 

 with the results obtained by Metschnikoff j: 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 Kolliker§, Metsch- 

 nikofFII, and Tschemofi"^. 



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.] 



• Broun's Klasseu und Ordn. Bd. iii. Abth. ii. p. 1324. 



t Beitr. zur vergl. Histol. p. 70, pi. iii. figs. 40 & 41. 



X hoc. cit. pp. .39 et seq. § Loc. cit. pp. 107 et seq. 



II Loc. cit. p. 53. f Bull, See. Imp. Nat. Mosc. 1869, p. 87, pi. i. 



