CERTAIN GENERAL CHARACTERISTICS 57 



able characteristics of reconstitutional patterns have been considered in 

 this chapter, but these have brought to hght certain points of interest. 



It is evident that, even though they finally become similar individuals, 

 the patterns of reconstitution in pieces from different body-levels are pri- 

 marily different and that these differences are, in general, graded in char- 

 acter and indicate graded differences of some sort in the parent body. 

 Except for failure of extreme apical or anterior regions to reconstitute 

 more basal or posterior parts and absence of head regeneration at the 

 more posterior body-levels in certain species, the differences in pattern 

 are quantitative, rather than qualitative or specific, differences in rate, 

 size, length, and proportion rather than in the kind of organs which de- 

 velop. These facts suggest that the differences are expressions of es- 

 sentially quantitative differences along the parent axes, whatever the 

 specific organ differences which may be present at different levels. If we 

 admit this, it follows that these quantitative differences in the parent 

 body are essential factors in determining developmental pattern in the 

 isolated pieces. 



Gradations or gradients of some sort, whose presence is indicated in one 

 way or another in development under natural conditions, are character- 

 istic of embryonic, as well as of other developmental, patterns. Considera- 

 tion of the question of their significance in embryonic pattern and of their 

 possible relations to the apparently specific regional differences in egg and 

 embryo, which are revealed by experimental procedures, is postponed un- 

 til other experimental data bearing upon the problem of pattern have 

 been presented. 



