PATHOLOGIC OVA, ALBINO RAT 119 



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 

 Eiern der Wirbeltiere sind spontan entstandene, das heisst, ohne ex- 

 perimentelle Eingriffe veranlasste Mehrfachbildungen ausserordentlich 

 selten, bei manchen Klassen iiberhaupt noch nie beobachtet worden, 

 dagegen sind sie relativ haufige Befunde bei manchen untersuchten 

 Arten von Knochenfischen und Vogeln, besonders bei der Forelle und 

 beim Hiihnchen. 



So far as I am aware, the possibility of hemiembryos in Mam- 

 malia 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. 



