OF THE CHORDA DORSALIS. 1 1 



usually largest in the centre, and becoming somewhat smaller 

 towards the outside. They have an irregular polyhedral shape, 

 mostly with spherical surfaces, which are sometimes convex 

 towards the outside, sometimes towards the cavity of the cell. 

 Their walls are very thin, colourless, smooth, aud almost 

 completely transparent, firm, and slightly extensible. They 

 dissolve readily in caustic potash. The rudiments of the 

 chorda dorsalis in the conical interstices of the vertebne of 

 cartilaginous fishes are not dissolved by dilute or concentrated 

 acetic acid. The chorda dorsalis of fishes according to J. Miiller 

 does not become converted into gelatine after long boiling. 

 The cells of the chorda dorsalis of frog's larvae contain in their 

 interior a colourless, homogeneous, transparent fluid, which 

 does not become cloudy at a boiling heat ; the slight clouding 

 observed in the chorda dorsalis after boiling, appears to be 

 situated more in the cell-walls, which afterwards appear mi- 

 nutely granulated. 



In the larva of Pelobates fuscus another formation occurs, 

 inasmuch as by far the greater proportion of these cells contain 

 a very distinct nucleus. It has the appearance of a somewhat 

 yellowish-coloured small disc, of a roundish oval form, rather 

 smaller than a blood-corpuscle of the frog, and almost as flat. 

 (See plate I, fig. 4 a, where it is represented from the chorda dor- 

 salis of Cyprinus erythrophthalmus.) In frog's larvae the nucleus 

 is nearly twice as large. It has a sharp, dark margin, and ap- 

 pears minutely granulated. In this little disc may be seen one, 

 rarely two, and very seldom three dark, sharply circumscribed 

 spots. It thus entirely resembles, both as a whole as well as in 

 its modifications, the cytoblast of vegetable cells with its nu- 

 cleolus, and microscopically, cannot at all be distinguished from 

 it. Compare plate I, fig. 4 «, with plate I, fig. 1 a. But it also 

 corresponds with it in its position in the cell. In very many 

 cells, the vertical wall of which is viewed from above, it may 

 be seen that the nucleus lies close on the inner surface of the 

 wall of the cell, or even embedded in the wall. It appears 

 then, as in plate I, fig. 1 a, only still somewhat flatter. I 

 have not, however, succeeded in observing that a lamella of 

 the cell-wall passes over its internal surface, which is also but 

 rarely seen in plants. If the external minutely granulated 

 cortical substance of the chorda dorsalis of Pelobates fuscus 



