ORIGINS OF EMBRYONIC PATTERNS 695 



to tension has been obtained by X-ray analysis.''" There is also evidence 

 of molecular orientation with respect to surfaces and interfaces. These 

 mechanical and surface orientations, however, may be in all possible di- 

 rections in a cell or a multicellular organism; consequently, it does not 

 appear possible that they can constitute the basis of axiate developmental 

 pattern. Protoplasms in general have not yet been shown to possess any 

 such structure that might serve as a basis for developmental pattern. 

 Evidence of the presence in eggs or other reproductive cells of a space 

 lattice related to developmental pattern is at present lacking. The pe- 

 ripheral cytoplasm of the egg of a sea urchin {Strongylocentrotus pur- 

 puratus) and, in the centrifuged egg, the zone of clear cytoplasm become 

 birefringent on fertilization, according to Moore and Miller (1937); but 

 this pattern can be only secondarily associated with developmental pat- 

 tern, for the egg possesses a polar, and probably a ventrodorsal, pattern 

 before fertilization. The cytoplasm of Amoeba is said to be birefringent 

 (W. J. Schmidt, 1937), but Amoeba has no persistent axiate pattern. 

 Evidence of orientation of elongated molecules in relation to direction of 

 protoplasmic flow has also been obtained in many cases. 



The hypothesis that the organism is fundamentally crystalline in char- 

 acter has been advanced in one form or another by various authors, and 

 similarities between organism and crystal have been pointed out repeat- 

 edly. Interpretation of the Bruchdreijachbildungen (see pp. 387-95) and 

 other features of development in terms of a hypothetical space lattice 

 has been attempted by Przibram."' Since the space lattice is entirely hy- 

 pothetical, it can, of course, be assumed to undergo the changes required 

 to account for the experimental results, and the required assumptions 

 are made for each case. Amphibian asymmetries and experimental rever- 

 sals have suggested analogies to crystals to certain authors.^' The ac- 

 cumulating evidence for existence of greatly elongated molecules and of 

 union of units, end to end, to form long chains — for example, in cellulose 

 and in various proteins — has been regarded by some as affording new 

 support for an essentially crystalline or paracrystalline basis for develop- 

 mental pattern. Seifriz, for example, in recent publications, holds that 

 there is in protoplasms a continuity of structure consisting of such elon- 

 gated molecules and that polarity and symmetry of organisms result from 



■I" E.g., Astbury, 1937, 1939; Astbury and Bell, 1938. 



•" Przibram, 1906, 1921, and other papers. 



^^ Spemann und Falkenberg, 1919; Harrison, 1921(7. 



