100 Transactions of the Royal Microscopical Society. 
In judging between the merits of these two explanations of the 
mode of development of the coloured blood-corpuscle, the first one 
might appear the most plausible and correct, if there remained no 
other phenomena to be accounted for. One of these phenomena is 
the presence of a considerable number of free nuclei in the circu- 
lating blood. Whether they are young nuclei, resulting from the 
division of older ones, subsequently surrounded by a layer of proto- 
plasm, or whether they have been only deprived of their layer of 
protoplasm, is difficult to decide. At any rate, in the blood of very 
young animals about five inches in length, the colourless blood- 
corpuscles are to a very great extent represented by these free 
nuclei. In examining the numerous transitory forms of develop- 
ment, represented in Fig. 42, we observe some of these free nuclei 
at a and c, the one oval, the other round ; h and d represent them in 
the act of division. Farther on at e, we meet with a round body 
limited by a dark single contour, and containing no granules what- 
soever, but moreover distinguished by an opaque centre and 
periphery, which are separated by a clear space in the form of a 
zone. Presuming that this body arose by a transformation of a 
free nucleus, it may be supposed that the granules in the interior of 
this nucleus were at first dissolved into a homogeneous substance, 
fusing with the wall, by which process the double contour would 
disappear ; and further, that subsequently a separation of this homo- 
geneous mass into a central and peripheral portion took place, from 
which finally a new nucleus and the dark-bordered granules, seen 
in the more advanced stages of metamorphosis, were found. 
Now it really matters not, whether this or the other explanation 
of the first stage of metamorphosis of the colourless blood-corpuscle 
into a coloured one be accepted as the correct one, as the resulting 
body in both instances consists of a mass of dark-bordered granules 
of a greenish tint, with a nucleus in its centre, and limited at the 
periphery by a distinct and dark contour. In the blood of the 
adult animal this body appears mostly round (Fig. 40, h, c, and d), 
while in that of very young animals it is oval (Fig. 42, / and y). 
The next stage of transition consists in the gradual disappearance 
of the dark-bordered granules (i, Tc, I, and m), and the appearance 
of a pale yellow colour in place of the greenish tint. 
In the pulp of the spleen, enclosed, as in the higher orders of 
aninoals, in meshes formed by a delicate fibrous tissue, the same 
forms of colourless blood-corpuscles are observed as in the circu- 
lating blood (Fig. 41). 
In the blood of very young animals the fully-developed 
coloured blood-corpuscles present the same characters as those of 
the adult. They are somewhat smaller, especially in breadth, and 
the nucleus appears more distinct, showing clearly its double 
contour (Fig. 43). 
