92 PATTEN. [Vou. XII. 
theory, or, at least, not in its widest sense, but only against 
the rigid limitations placed on it by Weismann and others. 
It is well known that an embryo may, under stress of new 
environment, divide and produce two or more new ones ; and 
perfectly formed embryos are produced from fragments of 
segmenting eggs, but these embryos have suffered either a 
diminution tn size, or in vitality, or both. No one, so far as I 
know, has succeeded in raising a fraction of the original ovum 
into a mature individual showing the same longevity and 
vitality as those raised from whole ova. The same is true of 
double or triple embryos produced by excessive growth. 
If we assume with Weismann that the material for two or 
more embryos is present in each egg that is capable of producing 
multiple embryos, and that the stimulus of the environment has 
called them all into activity, it will be difficult to explain how 
it happens that the newly formed parts disappear so soon after 
formation, and also—a difficulty that, so far as I know, has not 
been foreseen before — why the new material should be in tso- 
lated halves of different individuals instead of in one or more 
entirely new individuals distinct from the old, or why these 
halves should develop and unite with the old ones in the way 
they do. 
It is probable that the same method of forming the new 
parts in multiple embryos of Limulus is followed in other 
animals, only it has not been recognized there, because the 
embryological processes are more obscure. 
It should also be observed in this connection that there is 
no evidence that the new organs come from some indifferent 
reserved cells. In addition to the fact that, under very favor- 
able circumstances, no trace of such cells can be seen, it would 
be difficult to explain why they should always first manifest 
themselves at the point of greatest specialization, that is, at 
the very anterior median line, and grow backwards instead of 
forwards. We should, on the contrary, naturally look for 
them at the posterior end, and expect that they would produce 
a new embryo there in the usual manner. 
It seems to me that we must assume that in all normal ova 
there is a definite quality and quantity of formative material 
