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Prof. W. Salensky on the 
appears ; at the same time the latter assume a polygonal form, 
in consequence of the reciprocal pressure of adjoining cells, 
and grow more and more like the blastomeres. The constitution 
of the protoplasm of the kalymocytes presents a more lasting 
characteristic, which distinguishes these cells from the blasto- 
meres. Thisis, however, not constant, and in time this character 
too disappears. We have remarked above that vacuoles appear 
at a tolerably early period in the protoplasm of the kalymocytes; 
their number continually increases with the progress of 
development, so that in the stages at which the embryo con- 
sists of several hundred cells the protoplasm of the kalymo- 
cytes appears as a perfectly transparent viscid mass, traversed 
in different directions by a finely granular network of threads 
of the original substance. In consequence of this the kaly- 
mocytes of these stages appear paler in stained preparations 
than was formerly the case. Simultaneously with this the 
constitution of the protoplasm of the blastomeres also under- 
goes a change, in that it loses its previous finely granular 
structure, and appears more and more homogeneous and 
transparent. 
From this we see that the changes of the blastomeres go 
hand in hand with those of the kalymocytes. In both cases 
the result is a clarification and liquefaction of the protoplasm. 
If we consider at the same time that the differences in size 
between the blastomeres and kalymocytes gradually fade 
away, it follows that in the final stages of segmentation the 
two kinds of cells, kalymocytes and blastomeres, of which the 
segmented nucleus consists, must look precisely alike. As a 
matter of fact, if we examine a section from the later segmen- 
tation-stages of the oosperm of Pyrosoma , we find that the 
embryo consists of a large number of cells of precisely similar 
structure. Kalymocytes are no longer to be distinguished 
from blastomeres. Since in the subsequent stages of develop- 
ment all the cells of the embryo take an equal part in the 
formation of the cyathozooid, we arrive at the conclusion that 
the cyathozooid is formed from two different elements : — 
(i.) from the derivatives of the fertilized egg-cell — the blasto- 
meres, which throughout the whole of the animal kingdom 
alone play the part of formative elements ; and (ii.) from the 
non-fertilized elements — the kalymocytes, which unite with 
the former and assume the role of the formative elements. 
The processes of development in the ovum of Pyrosoma 
wdiich I have just described, in spite of their peculiarity, are 
not entirely unique in the series of developmental phenomena 
which have been discovered in the animal kingdom in recent 
times. The nearest approach is made by those described by 
