4 PATTERNS AND PROBLEMS OF DEVELOPMENT 



uals; an "organism" is a system of protoplasms, an order and pattern ap- 

 parently on a larger scale than that of a protoplasm. The most general 

 characteristic of organismic pattern is a surface-interior difference, and in 

 some simple organisms such difference apparently constitutes the only 

 persistent organismic pattern, though other patterns may be temporarily 

 superimposed on it. In Amoeba, for example, pattern is apparently pri- 

 marily surface-interior; but the formation of a pseudopod alters and com- 

 plicates the pattern temporarily, and in some cases the whole body may 

 become temporarily an anteroposterior pattern with activity of a single 

 pseudopodial region dominating it. Environmental factors are apparently 

 directly concerned in the origin of surface-interior pattern. The surface of 

 the protoplasm exposed to the external medium or in contact with other 

 systems like itself, as in multicellular tissues, becomes different from the 

 interior. The characteristics of the cell nucleus and its relations to the 

 cytoplasm suggest that it originated as a differentiation of the interior. 

 Nuclei or their parts may possess a very definite pattern, but this pat- 

 tern is not the pattern of the organism or the cell and apparently cannot 

 autonomously determine that pattern. At present there is no ground for 

 believing that even surface-interior pattern can arise independently of 

 environment. 



AXIATE PATTERNS 



In most organisms we find, in addition to surface-interior pattern, other 

 orders or patterns which biologists have been accustomed to distinguish as 

 polarity, radial and bilateral symmetry, ventrodorsality, dorsiventrality, 

 and various asymmetry patterns. A polarity is a single serial order in a 

 certain direction, referable to an imaginary polar axis. Symmetries and 

 asymmetries may be regarded as polarities in other directions, referable 

 to other axes — radial, ventrodorsal, dorsiventral, lateral — or in other di- 

 rections in organ systems. On the other hand, polarity is an asymmetry 

 in a certain direction. In other words, the different directions to which the 

 spatial orders of organismic pattern are referable do not necessarily repre- 

 sent fundamentally different features of pattern. The terms "polarity," 

 "symmetry," and "asymmetry" merely provide convenient distinctions 

 for patterns in different directions in the developing organism,. the term 

 "polarity" usually being applied to the order which becomes evident first 

 in development or is most conspicuous, with "symmetry" and "asym- 

 metry" applied to secondary orders in other directions, usually becoming 

 evident under natural conditions later in development than polarity. It 



