1894,} Embryology. 275 
The development of the uninjured half of the egg is not as it would 
be in an entire egg but is so modified by the presence of a partly dead 
mass adjacent to it that it produces what may be called rather an ab- 
normal blastula with an inclusion of inactive or dead yolk than in any 
sense a half-blastula. 
Later, abnormal gastrulas are formed. These, however, are not 
Semigastrule laterales, anteriores or posteriores as Roux describes, but 
gastrule checked and distorted in their formation. 
It seems, moreover, that only the presence of the inactive or dead 
yolk of the injured cell prevents the living cell from developing into a 
complete small gastrula as in the echinoderm experiments of Driesch. 
This dead or injured mass remains intimately attached to the live cell 
and hence is incorporated as a part of the embryo which it modifies 
somewhat as the yolk of a meroblastic egg modifies the part that forms 
the embryo. 
Some eggs develop even the medullary folds and the notochord and 
form parts of larve. These are, however, very incomplete and also 
much varied in character; since, apparently, the injured cell is killed, 
coagulated, only in the part near the needle hole and may become, else- 
where, utilized as part of the embryo, this embryo will be more or less 
perfect according as the needle thrust has destroyed more or less and 
even according as it has destroyed one part or another of the cell, for 
thus the dead part will come to occupy a ventral or a dorsal position, 
etc., in the embryo. 
This description of the formation of embryos that are more or less 
complete, according as the mass of inert substance is less or greater, is 
strongly opposed to the conception of Roux that, namely, the half egg 
first formed a half embryo. Yet Roux allowed that a more complete 
embryo was subsequently formed from the half by a process of revivi- 
fication of the inert half, by what he called postgeneration. The ulti- 
mate result is thus the same according to either investigator. 
Moreover Hertwig concedes that some process of “ postgeneration ” 
takes place to convert part of the inert mass into active cells; the in- 
jury to the cell having been in part but temporary so that it may later 
take part in forming the embryo. : 
While Roux insists upon the power of one cell to develop by itself 
as a half embryo and then to coerce the inactive half into the subse- 
quent formation of the complete embryo, Hertwig lays stress upon the 
continuity and uniformity ot a process that is from the first a forma- 
tion of a whole embryo by the half-egg, subsequently, in part, assisted 
by the slow acting injured half. 
