452 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. KolUker. 



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 imtrition 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 laminae, 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, 

 accordhig to which the organs of hearing make their appearance in 

 the form of compact and solid bodies. He asserts that in the Sepiolce 

 the formation of these organs presents a complete parallelism with 

 what we know of their development in the Vertebrata. As to the 



