PROBLEMS AND MATERIAL 3 



with power of free choice, underlying and guiding development, we should 

 expect to find fundamental similarities of pattern in all of them. In any 

 case, there is in all a definite developmental pattern involving spatial and 

 chronological order and physiological integration. There is reason to be- 

 lieve that the view so widely current, either implicitly or explicitly, that 

 embryonic development is of primary, and all other forms of development 

 of secondary, importance, has in some measure led us astray in concen- 

 trating much of our attention on problems concerned with this form of 

 development alone rather than on the problem of developmental pattern 

 in general and the question what, if any, features of developmental pat- 

 tern are common to all forms of development. By every criterion which we 

 can apply, the oocyte and the spermatozoon are highly specialized and 

 dift'erentiated cells. Evidently the differentiation of the egg cytoplasm is 

 a factor in determining the course of development of the embryo : ascidian 

 embryonic development is an excellent example. But, as noted above, an 

 ascidian can develop in various other ways from other starting-points — 

 from buds, pieces of body or stolon, etc., which certainly differ in organiza- 

 tion from the egg and from each other. Embryonic development in a par- 

 ticular species under natural conditions always has the same starting- 

 point, the egg, which always, except for genetic potentialities, has the 

 same organization in a particular species. It seems beyond question that 

 embryonic development is a relatively highly specialized form of develop- 

 ment. If this is true, there is undoubtedly much to be learned concerning 

 the fundamentals of developmental pattern from the bud, the piece, and 

 other forms of development, as well as from the egg. May we not hope to 

 attain a more adequate conception of development by including in our 

 analysis other forms of development as well as egg and embryo? May it 

 not even be possible to interpret certain features of embryogeny in the 

 light of what we learn from other forms of development? 



Any consideration of the physiology of development, if it is to be more 

 than a mere compilation of data, must itself have an order and pattern 

 and be integr3,ted into a whole. The ordering and integrating factors in 

 the following pages are the problems of pattern, order, and integration, 

 particularly in the earlier stages of development. 



THE PROBLEM OF ORGANIZATION 

 rROTOPLASM AND ORGANISM 



A "protoplasm" is a complex physicochemical system differing in 

 constitution in different species and, to some extent, in different Individ- 



