PROLEGOMENA 



The Sciences, unlike the Graces or the Eumenides, are not limited 

 in number. Once born, they are immortal, but, as knowledge in- 

 creases, they are ever multiplying, and so great is now the dominion 

 of the scientific mind that every few years sees a new one brought 

 into the world. Some spring, fully armed, from the brains of one or 

 two men of genius, but most of them, perhaps, come only gradually 

 to their full development through the labours of very many obscure 

 and accurate observers. 



If the analogy may be permitted, physico-chemical embryology has 

 so far been living an intra-uterine existence. Its facts have been 

 buried in a wide range of scientific journals, and its theories have 

 lain dormant or in potentia in reviews of modest scope. Physico- 

 chemical embryology has, indeed, arrived at the stage immediately 

 priox to birth, and all it needs is a skilful obstetrician, for, when once 

 it has reached the light of day and has passed for ever out of the 

 foetal stage, it will be well able to take care of itself. This obstetrical 

 task is that which I have chosen and obviously enough it divides 

 into three principal heads: first, to collect together out of all the 

 original papers on the subject the facts which are known about the 

 physico-chemical basis of embryonic development; second, to relate 

 these facts to each other and to the facts derived from the labours 

 of investigators in morphological embryology and " Entwicklungs- 

 mechanik," and, third, to ascertain whether, from what is at present 

 known, any generally valid principles emerge. 



I may as well say at the outset that in order to do this certain 

 arbitrary boundary-lines are inevitable. The following arrangement 

 has been adopted. Chronologically speaking, the prelude to all em- 

 bryonic development is the maturation of the egg-cell, but this is not 

 strictly embryology, and so has been relegated to an appendix. The 

 egg-cell as a physico-chemical system is dealt with at the opening 

 of Part III, and thereafter the physico-chemical aspects of develop- 

 ment follow in order. No mention will be made of fertilisation, for 

 this has been treated exhaustively by other writers (Lillie, Dalcq) 

 and, after all, embryology presupposes fertiUsation whether natural 

 or artificial. Nor in later chapters will any complete treatment be 



