ORGANISM AND MECHANISM 127 



When we take the most familiar case of all, the development 

 of the chick in the course of twenty-one days from a miinite 

 drop of living matter lying on the top of the yolk — the 

 gradual emergence of the obviously complex from the ap- 

 parently simple — we feel how true it is still, what Harvey 

 wrote three centuries ago: — ^'Neither the schools of physi- 

 cians nor Aristotle's discerning brain have disclosed the man- 

 ner how the cock and its seed doth mint and coin the chicken 

 out of the egg." It is not surprising that the facts of genera- 

 tion and development have often led naturalists to the con- 

 clusion that the categories of mechanism fall short in the 

 domain of the organic. What particular facts of devel- 

 opment seem to require more than mechanical description ? 

 There is the condensation of the inheritance into the micro- 

 scopically minute germ-cell — an extraordinary telescoping of 

 individuality, of which we can form no image. It is quite 

 true that there is within egg-cells a demonstrable complexity 

 of organisation far greater than used to be supposed, that 

 the nucleus is a little world in itself, that there is a 

 growing knowledge of extremely minute, yet often distinc- 

 tive, organ-forming plastosomes in the cytoplasm of the eggy 

 that the artificial removal of part of the egg-cell is sometimes, 

 as in Ascidians, followed by the non-development of a partic- 

 ular structure in the embryo, and so on. More and more 

 we are coming to see in the germ-cell an implicit individ- 

 uality with complex and specific organisation. But no sooner 

 have we got this idea clearly focused in the mind than we 

 are confronted with such facts as those of merogony, that 

 a fragment of an egg-cell is able to develop into a nonnal 

 embryo. It may be an argumentum ad ignorantiam, but 

 if it be held, as the mechanists hold, that the egg-cell is 

 completely describable as a chemico-physical mechanism of 



