237 
of an Echinus egg contains all the determinants or formative sub- 
stances for the complete adult, since its parts (if it be divided in 
any way) can give rise to a whole embryo. It is inconceivable that 
there could be present in the protoplasm of any part of a sea- 
urchin’s egg an individual and distinct chemical substance for every 
different part of the complex adult. To meet this difficulty, how- 
ever, it has been assumed by some recent writers that there is only 
one chemical substance or very few to begin with and that these 
determine the development of other organ-forming substances later. 
The development of the egg of Cynthia is supposed to give much 
support to this theory. 
If we consider that by the chemical changes or disintegration 
of a complex chemical compound (or a few complex chemical com- 
pounds) a definite sequence of events follows, resulting in the de- 
velopment of organic form, then how are we to explain the regenera- 
tion of lost parts in adult or embryonic organisms'? Whence comes 
the re-existence of the compound or the “chemical state” to repeat 
its sequence when this has been completed once already? 
It is to my mind quite illogical to assume, as MacRride has done, 
that the development of Cynthia proves the coloured masses to be 
definite organ-forming substances 1 : — “In the egg of Cynthia 
partita Nature has provided us with an ocular demonstration of the 
existence of organ-forming substances.” If Conklin’s experimental 
work is considered final enough to prove that parts of the segment- 
ing egg are unable to regenerate the other parts, it does not prove 
that the coloured substances are organ-forming substances, nor that 
organ-forming substances alone can explain the organised develop- 
ment of form in the embryo. 
What we see in the embryology of Cynthia suggests that the 
phenomena of development are accompanied by chemical reactions. 
This does not, however, necessitate the assumption that these same 
chemical reactions are the actual organising and controlling factors 
of development. Three differently coloured substances are present 
in the egg of Cynthia which are separated in development, and which 
appear to be associated with the production of certain parts of the 
embryo. It is possible that these substances are used in the con- 
struction of certain parts of the body without being in any sense 
factors of causation. Thus, as a matter of fact, the term organ- 
forming substances” may be strongly criticised, for substances pio- 
bably do occur which are used in the formation of organs without 
being the cause of formation of those organs. The metal of which 
church organ pipes are composed is an organ-forming substance, 
but we may put down in a heap, metal, wood, ivory, and reeds, and 
we shall never see them arrange themselves into a church organ. 
I have devoted some little time to this discussion of the develop- 
ment of 1 lie organism. To what has it led? According to Driescn 
we are to conclude that something is present in the egg to co-ordinate, 
1 MiicBride. Text Book of Embryology. Vol. I. pp. 631, 632. 
