PATHOLOGIC OVA, ALBINO RAT 363 
nuclei, perhaps indicating altered metabolism in the two blasto- 
meres. I am inclined to think that both of these cells would 
have degenerated in the course of further development; however, 
their fate can only be guessed and not predicted. The possibility 
of their developing into half embryos is suggested. Half embryos 
developing as a result of a separation of the first two blastomeres 
has not been observed in the Mammalia, and an experimental 
test of the question is for the present not a probability. 
As a result of experimental embryology it has been clearly 
shown that through mechanical interference polysomatous mon- 
sters may be produced from normal ova. The first two blasto- 
meres are totipotent, as expressed by Driesch. Driesch was 
able to produce polysomatous forms by mechanical separation 
of the first two blastomeres in sea urchin eggs; Wilson, by sepa- 
rating through shaking of 2- and 4-cell stages in Amphioxus; O. 
Hertwig, Herlitzka and Spemann, by separating the first two 
cells in amphibian eggs; O. Schultze and others, by use of gravity 
and compression; and Loeb and others by use of chemical agents. 
By various means, then, when suitably applied and at the right 
time, hemiembryos have been produced by separating or poten- 
tially separating the first two blastomeres in certain forms. O. 
Hertwig states: 
Bei den kleinen, mit geringen Mengen von Dotter ausgestatteten 
Hiern der Wirbeltiere sind spontan entstandene, das heisst, ohne ex- 
perimentelle Eingriffe veranlasste Mehrfachbildungen ausserordentlich 
selten, bei manchen Klassen tiberhaupt noch nie beobachtet worden, 
dagegen sind sie relativ haufige Befunde bei manchen untersuchten 
Arten von Knochenfischen und Végeln, besonders bei der Forelle und 
beim Hiihnchen. 
So far as I am aware, the possibility of hemiembryos in Mam- 
mala has not been shown. In the albino rat, the oolemma 
may be lost as early as the 2-cell stage. In forms with early 
loss of oolemma, the separation of the two first blastomeres does 
not appear to me as an impossibility. The probable fate of sepa- 
rated mammalian blastomeres can only be conjectured, since it 
is manifestly impossible, for the present, to follow them in 
further development. 
