Blood-corpuscles of A. tridactylum, &c. By Dr. Schmidt. 103 
But one of the most interesting facts which I observed in the 
blood of these embryos, and to which I wish to direct the attention 
of other observers, was the entire absence of the colourless blood- 
corpuscles ; not a single one could be found. And this fact corro- 
borates what I formerly asserted in my paper “ On the Origin and 
Development of the Coloured Blood-corpuscles in Man,” published 
in the ‘ Monthly Microscopical Journal ’ of February, 1874, namely, 
that the blood of the embryo contains no colourless blood-corpuscles 
prior to the development of the spleen or lymphatic glands. 
The particular view regarding the structure of the coloured 
blood-corpuscles of Amphiuma tridactylum, which I formed after 
comparing the facts elicited by the microscopical examinations of 
these bodies, I have already partly exposed in the preceding portion 
of this paper. It corresponds in its chief points with that which I 
have entertained and expressed before. The following represents a 
summary of the conclusions to which I finally arrived. 
The coloured blood-corpuscle in question, as well as that of other 
Amphibia, represents an organic cell, consisting in its normal condi- 
tion of a homogeneous protoplasm, surrounding a nucleus. That 
part of the protoplasm forming the outer surface of the blood-cor- 
puscle seems to be of a greater density than the rest. In conse- 
quence of this circumstance, a membrane-like stratum or layer 
(membraneous layer) is formed, possessing no distinct inner limita- 
tion, as would otherwise be indicated by the presence of a distinct 
second contour, but maintaining its connection with the underlying 
protoplasm by its homogeneousness of composition. In the fresh 
condition the membraneous layer is seen in the form of a clear, 
narrow border of a greenish tint. But when the protoplasm 
surrounding the nucleus and underlying the “ membraneous layer ” 
becomes dissolved, or otherwise altered by the action of water or 
other reagents, this layer assumes the appearance of a distinct cell- 
wall, characterized by the presence of a distinct double contour. 
The colouring matter (haemoglobin) of the blood-corpuscle does not 
seem to be chemically united with the protoplasm, but to exist 
rather in the form of an intimate mixture with the latter, similar 
to that of the oxygen and nitrogen composing our atmosphere. In 
this form it exists, either equally distributed throughout the whole 
mass of the protoplasm, or, judging from my observation, repre- 
sented in Fig. 13, perhaps only in the form of a stratum beneath 
the membraneous layer. The latter supposition remains an open 
question. Whether the haemoglobin penetrates the membraneous 
layer I am not prepared to decide. The readiness with which the 
colouring matter escapes from the blood-corpuscles, even by the 
action of very weak reagents, such as water or some gases, seems to 
indicate that the mutual connection between the haemoglobin and 
the protoplasm is of a feeble nature. 
