OF THE CHORDA DORSALIS. 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, and 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 vertebra of 
cartilaginous fishes are not dissolved by dilute or concentrated 
acetic acid. The chorda dorsalis of fishes according to J. Miller 
does not become converted into gelatine after long boiling. 
The cells of the chorda dorsalis of frog’s larve 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. 4a, where it is represented from the chorda dor- 
salis of Cyprinus erythrophthalmus.) In frog’s larve 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. 4a, with plate I, fig. la. 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 
