264 EXPERIMENTS AND OBSERVATIONS 
the unyolked ova is much vacuolated ; this occurs only when some 
preserving agent containing much nitric acid has been used, such 
as Perenyi’s mixture or picro-nitric acid, and is due to the action of 
the nitric acid. 
Several investigators have expressed the conclusion that the 
vitelline nucleus is connected with the formation of the yolk,—is the 
centre, in fact, at which this process takes place. This is a suggestion 
which one would be glad to accept if possible, because it would afford 
a satisfactory explanation of the presence of this body, otherwise so 
difficult to understand. A very interesting and useful examination 
of the problem from this point of view is contained in the account 
given by Professor Emery of the history of the egg of Fierasfer in 
his monograph on that genus published by the Zoological Station of 
Naples. In many respects I find Professor Emery’s observations 
and views much more in agreement with my own than those of 
other authors who have considered the development of the egg in 
fishes. In my judgment he shows a sounder and more compre- 
hensive grasp of the succession of appearances to be interpreted, 
and has no inclination, hke many others, to form extraordinary con- 
clusions inconsistent with the general view of the nature of the egg, 
and supported by scarcely any evidence. 
Emery’s description of the earlier history of the vitelline nucleus 
agrees, to a great extent, with mine. It appears, he. says, as a 
small mass of granulations excentrically situated, and then becomes 
larger and denser, but never acquires a definite boundary. Its 
ultimate history consists in its gradual disintegration with the 
formation of the vitelline spherules. The granular vitelline nucleus 
assumes an irregular form, more or less stellate, and often shows in 
its interior one or two small clear vacuoles. Around the nucleus 
extends an obscure zone, semilunar in section, of very minute 
granules, the beginning of the formation of the vitelline globules. 
This zone continually extends and surrounds the whole ovum, and 
as the yolk-globules get larger the vitelline nucleus becomes merely 
a small clear space in the layer of formed yolk. Emery goes on to 
say that it is not clear from these facts whether the yolk-globules 
are formed exclusively at the expense of the vitelline nucleus, or in 
part from this and in part directly from the plasma of the ovum, or 
if, lastly, the vitelline nucleus is formed and disappears without its 
substance contributing to the production of the yolk. 
Emery, then, was not able to decide in what way the vitelline 
nucleus is connected with the formation of the yolk-globules, but he 
states that the development of these globules commences in Fierasfer 
in the immediate neighbourhood of the nucleus and extends outwards. 
It should be noted that the eggs of Fierasfer are, when mature, 
