470 Prof. 8. Apathy on 
of development, can be rediscovered in ontogeny also, and 
indeed both among the Protozoa and the Metazoa as well. 
The ontogeny of a Metazoon individual does not commence 
with the stage of the fertilized or unfertilized egg-cell in 
process of division from which the Metazoon is built up ; 
but the individual itself, which is represented by the mature 
ege-cell, has a past of its own which was possibly of great 
length, and which commenced with the non-nucleate stage 
within that germ-cell, from whose division into two it imme- 
diately proceeded as an unripe egg-cell. 
I am unacquainted with any facts—it may be that my 
knowledge is insufficient for the purpose—which would 
render the theory of morphogeny inapplicable to the Protozoa, 
especially as, between the visible stages of the development 
of their organization, there may be others which are invisible. 
Development may even attain the highest stage of unicellular 
existence without evolving further organization ; for it con- 
sists in a series of transformations of the PROPERTIES of the 
Protoblast, in imitation of the sequence of events in the 
phylogeny, wherein each arrangement of organs corresponding 
to the particular stage of development is only potentially 
combined with the succession of these transformations—that 
is, the latter includes only the capacity to produce such organ- 
ization should circumstances require it. 
In this manner it seems to me that the egg-cell ontogeneti- 
cally arrives at the highest stage of unicellular existence 
which has been present in the phylogeny of that form of life ; 
and all its daughter-cells and subsequent descendants, the 
constituents of the Metazoon body, have the capacity to reach 
the same stage, and must endeavour to reach it by the same 
way, starting from the stage of the non-nucleate Protoblast. 
The rapidity of the development varies according to the con- 
ditions under which the particular cell commences and con- 
tinues to maintain its individual life. The greater portion of 
the cells of the Metazoon body, however, owing to the con- 
ditions which obtain at an earlier or later stage of the onto- 
geny of the latter, is compelled actually to develop the 
organization which belongs to this particular stage, although 
it may not be exhibited by other cells of the body. Those 
cells which, at whatever stage, really have to develop their 
organization, are hindered in their potential further develop- 
ment owing to immediate one-sided adaptation, are usually 
enfeebled in consequence of the performance of special func- 
tions, and never attain the highest stage of development, to 
which at their origin they were, so to speak, historically 
predestinated. It is only the reproductive cells, or, if two 
