480 Prof. S. Apathy on 
The further ontogeny of Salinella also, subsequent to the 
already active unicellular stage, exhibits nothing extraordi- 
nary. Frenzel writes:—‘ For it is precisely the further 
development of this larva, incomplete though my study of it 
was, which proves that it does not develop into the perfect 
animal by means of ordinary division, much as a colony is 
formed from a single Choanoflagellate, but by a far more 
complicated process, which we may most fitly term endo- 
genous cell-formation.” We may, however, designate the 
segmentation of all Metazoa whatever, and even the formation 
of the daughter-colonies of the Volvocinesxs, as endogenous 
cell-division (“ cell-formation”’). In very many cases the 
ege-cell has a distinct cell-membrane, and the processes of 
fission, in which segmentation consists, always proceed 
within this membrane; it often happens that it is only the 
already tolerably advanced larva or the almost perfect animal 
that leaves the cell-membrane of the parent-cell, the egg-cell. 
Even more distinct endogenous cell-division than in the case 
of the holoblastic ova is the segmentation in the meroblastic 
eges, where, as for instance in the egg of the fly, the limits 
of the daughter-cells within the cell-membrane of the parent- 
cell are for a long time absolutely indistinguishable from one 
another. 
It is indeed in the chief degree the circumstance that the 
daughter-cells remain in organic connexion with one another, 
and that they have no longer the strength to separate, which 
has replaced societies of cells by the higher category of 
colonies ; and a still more intimate union of the cells, in 
connexion with their endogenous origin in the egg-cell and 
in consequence of their further individual . debilitation, 
characterizes the Metazoa, and makes of them a single indi- 
vidual, an indivisible physiological whole. 
That the daughter-cells and subsequent descendants of the 
Metazoon egg-cell have now no longer the power to separate 
from one another, and lead an independent cell-life like Pro- 
tozoa or like the unicellular ancestors of the species, is a fact. 
It remains to be asked, what is the cause of this? It cannot 
be a change of habit owing to the living together for so long 
in the cell-colonies of the ancestors, for the latter is itself the 
first consequence of the cause for which we are seeking. I 
consider that the cause is to be found in a certain debilitation 
of the genus of Protoblasts with which we have to deal; and 
the latter is again nothing more than the consequence of that 
change in all protoplasms (vital qualities) which sets in as 
time goes on, even without special external influences, and 
which we are only able to detect through its combined effect 
