PHYSIOLOGICAL GRADIENTS. 149 



great difficulties to any preformistic conception of organismic 

 pattern, for protoplasmic pattern alone does not appear to afford 

 any basis for the origin of this pattern of a much higher order 

 of magnitude. Apparently organismic pattern is in some way 

 superimposed on protoplasm and unless we are content to accept 

 the " vitalistic " conclusions as a solution of the problem, we are 

 forced to believe that in the final analysis organismic pattern 

 arises in some way through the relations between protoplasm 

 and the external world. 



Second, organismic pattern as regards its more general fea- 

 tures is apparently to a large extent independent of the specific 

 differences in constitution of the different protoplasms. This 

 independence is clearly indicated by the fact that only three types 

 of spatial order appear in organismic pattern. These three are 

 the surface-interior, or centered pattern in which the order is 

 spatially referable to a point, the axiate pattern, in which the 

 order is referable to a line, the axis, and the bilateral pattern, in 

 which the order is referable to a plane passed through the line 

 representing the axis. The spatial plan or pattern of all organ- 

 isms represents either some one of these patterns or some modi- 

 fication or combination of one or more of them. If organismic 

 pattern were inherent in protoplasm and therefore determined 

 entirely by its specific hereditary constitution we should expect 

 a far greater diversity in the general spatial order in organisms. 

 The diversity appears, however, not in the general pattern but 

 in the character and course of differentiation of its parts, and 

 the degree and character of physiological relation between them. 

 The liverwort MarcJiantia and the flatworm Planaria are both 

 axiate and bilaterally symmetrical, i.e., the general spatial pattern 

 is essentially identical in both, but they are very different organ- 

 isms because the materials, the protoplasms, in which the pattern 

 exists are very different in constitution. Likewise different 

 species of liverwort and different species of planarians differ in 

 definite and characteristic ways because, even though the gen- 

 eral features of the liverwort pattern or the planarian pattern are 

 the same in all, the pattern is so to speak worked out or devel- 

 oped in specifically different protoplasms. And finally, both in 

 individual development and in evolution we find in general a 



