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1879.] ; 207 [Minot. 
I regard it as probable that the alterations in the size, shape, and 
position of the nucleus, which is at first spherical in form and central 
in position — that these alterations also proceed according to fixed 
laws, but I have obtained no satisfactory results. 
6. The primitive cells of the mesoderm are amoeboid in character. 
For all mesodermic cells, not mechanically united to other cells, but 
capable of independent locomotion by amoeboid movements, I propose 
the collective name of mesamoeboids — as a term at once appropriate 
and corresponding to a natural class of tissues. The mesamoeboids 
then I regard as the primitive form of the cells of the mesoderm, 
thus implying that when amoeboid cells are found in the higher 
Metazoa, we are dealing with those mesodermic elements which 
have been least modified in the course of development. According 
to this view the wander cells and white corpuscles in vertebrates re- 
present the earliest condition of the mesoderm. To prove this thesis 
it must be demonstrated (1) that in the lowest Metazoa the cells of the 
middle layer are mainly amoeboid in form, and (2) that the mesoderm 
is formed in the young embryo of the Metazoa as a collection of 
amoeboid cells. Both these demonstrations can, I think, be partially 
made by reference to observations already published. I have myself 
made observations which confirm my views, and indeed, it was while 
examining a specimen of Grantia that the importance of “ mesamoe- 
boids” first struck me. 
A. That the middle layer of the sponges consists mainly of 
amoeboids cells is now a familiar fact, thanks to the brilliant inves- 
tigations of F. BE. Schulze and others, and it is not difficult to confirm 
these observations. Schulze has shown that it is even from these 
cells that the sexual products arise. It has, however, not yet been 
shown that this layer is strictly homologous with the mesoderm. 
In the case of the Coelenterata, the mesoderm is formed from sev- 
eral sources, and includes : (1) the reproductive cells, (2) the muscular 
fibrillae, (3) gelatinous tissue, the cells of which are amoeboid in 
character. In these animals the histological differentiation of the 
spermatozoa, ova, and muscles precedes their separation from the 
ectoderm — and only a portion of the mesodermic elements exist in 
or pass through the mesamoeboid stage. We must therefore be cau- 
tious in attributing importance to the primary value of these cells. 
B. In the embryo of all metazoa higher than the Coelenterata, 
amoeboid cells are often the first mesodermic elements to appear. 
