EVOLUTION AND EPIGENESIS. 209 



tioned by Huxley, Brooks, Roux, Weismann, and others. I am 

 of the opinion that such comparison, especially as handled by 

 Bourne and Hertwig, is unwarranted and decidedly misleading. 

 It is the chief purpose of this and the two following lectures 

 to elucidate the more essential distinctions between our stand- 

 points and theories of development, and thus to remove some 

 misconceptions which have become rife. 



I should perhaps say at the outset that I have no theory of 

 development either to announce or to defend. It is of more 

 importance just now to have well-defined standpoints and clear 

 ideas of guiding principles. The foundations at least must be 

 made secure before we can profitably undertake to elaborate 

 the superstructure. The corner-stone on which most theories 

 of development now rest — the assumption that the germ- 

 plasm is exclusively contained in the nuclear chromosomes — 

 may not be so secure as some imagine. Let that stone be 

 upset, and what would become of all the hypotheses erected 

 on migrating pangens and disintegrating determinants } The 

 centrosome question has yet to be settled, and a much deeper 

 insight into the nature of protoplasmic structure is required 

 before we can safely locate the seat of heredity. The possibil- 

 ity — not to say probability — that the egg is frojn the begin- 

 ning of its existence as an individual cell definitely oriented, 

 has as yet received but little attention. Many difficult ques- 

 tions are involved which can only be settled after the most ex- 

 haustive analysis of its structure and the most careful exami- 

 nation of its entire history. It is not enough to catch a fact 

 here and there, in this or that species ; the whole series of 

 phenomena must be studied genetically, and in as many forms 

 as possible. It often happens that we have to snatch facts as 

 opportunity brings them within reach, regardless perhaps of 

 their connections ; but so long as they stand isolated, they are 

 unsafe pegs to hang theories upon. Examples abound on this 

 one question of the orientation of the ^g%, and the mention of 

 " isotropism" will recall more than one windfall of premature 

 speculations. 



As we have seen in the case of Bourne and Hertwig, who 

 represent fairly well the more moderate epigenesis of to-day, 



