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dimensional “machine” which has the characters of our machines of 
everyday life. We must look then at other chemical explanations 
which have been put forward. The best known is the Roux-Weiss- 
man, which assumes that a complicated structure built up of deter- 
minants, representing the characters to appear in development, is 
present in the egg, and that disintregation of the structure during 
development and the segregation of the determinants is responsible 
for the growth of the adult form. It will be obvious that 
this explanation alone fails to explain the experiments made 
by Driesch on the sea-urchin embryo. Removal of a blas- 
tomere should result in the loss of certain determinants or 
chemical substances, and consequently certain structures should be 
missing from the embryo. Subsidiary explanations have therefore 
to be added to account for these results and also for the phenomena 
of regeneration. The development of Cynthia would lend support 
to this theory if it were universal— but it isn’t. Moreover, the ex- 
periments on the egg of Cynthia do not prove conclusively that the 
bk istomeres have lost the power of producing complete embryos. 
The method of experiment alone may have prevented the full ex- 
pression of their growth taking place. Did not Roux’ famous ex- 
periment in 1SSS — the destruction of one blastomere of the two-cell 
stage in the development of the frog’s egg — appear to prove con- 
clusively the segregation of determinants'? Roux found that if one 
of the two first blast omeres was destroyed by means of a red hot 
needle, the other continued to segment and finally gave rise to a 
half embryo — either a right or a left half according to which blasto- 
mere had been destroyed. This result led naturally to the assump- 
tion that the first division of the frog’s egg was qualitative and sepa- 
rated the materials of the right half of the embryo from those for 
the left. Later investigations showed, however, that under other 
circumstances the two first blastomeres might give rise each to an 
embryo whose complete development was only prevented by the im- 
pediment offered by the presence of the other, whether living or dead. 
In the Newt, where the two first blastomeres can be separated, two 
whole larvae result. It is quite evident, therefore, that the potenti- 
ality of the two blast o.meres is a question of constitution plus some- 
thing else. The experiments on Cynthia egg's seem to me to be, 
something like those of Roux on the egg of the frog. It is not yet 
evident from them that loss of certain blastomeres causes incom- 
plete development because certain substances are lost. It is note- 
worthy that the blastoineres cannot be actually separated; it is only 
possible to kill different ones by means of a hot needle and note the 
development of the survivors. It is wonderful that the mutilated 
embryo is able to survive at all. 
Quite apart, however, from the above, if we allow the assump- 
tion of numerous determinants, we have to account for the manner in 
which they are ushered to their proper places, repressed, or im- 
pelled to develope. We have to explain how it is that every part 
