II. OiNTOGENY 351 



to regenerate and the individuals having the stronger regenerative 

 capacity might be able to survive the more, the character would be 

 more and more advanced until the present status of plants was reached. 

 The occurrence of proliferative changes following injury, however^ 

 is observable also in higher animlas though not so manifest as in 

 plants. Observations of Cooke et al. (23) on the changes which oc- 

 curred in excised rabbit and human skin after injury have shovv'n 

 that even after removal from body certain tissue elements may retain 

 the ability to react with proliferative changes in response to tissue in- 

 jury if kept under artificially stimulated physiological conditions. 



3. The Formation of Organs 



Unlike the growth of usual crystals, in the development of organ- 

 ism.s different shapes are developed on the different parts of the body 

 with the formation of a variety of organs. Fundamental principles to 

 induce such a dissimilarity was already discussed in Part IV, Chapter 

 VI, stating that the main factors involved in it are considered to be 

 hormones, which provide different stimuli to different parts of the 

 body, according to which different restricted structures are developed, 

 with the production of the complicated "crystal shape". 



If ^-stimulus is added -to a germinal cell having ^-structure, the 

 structure will be converted to B with the formation of the "crystal 

 shape" corresponding to ^-structure. In the same way, c-stimulus 

 will induce C-structure and its "crystal shape". In this case, B and 

 C are considered to be organs generated from A, the germinal cell, 

 and b and c are the hormones inducing the respective organs. A has 

 the "predisposition" to be changed into both B and C in responding 

 the respective stimuli, b and c. In other words, A recovers 5-struc- 

 ture under ^-stimulus, and C-structure under c-stimulus. As will be 

 mentioned later ^ is a structural complex, not a single structure. In 

 the following the matter will be considered in a less abstract way. 



As was mentioned already, protein structure is greatly influenced 

 by environmental factors. On the other hand, the surface of an Qgg 

 cell may not be similar with environmental factors, such as gravita- 

 tion, light, and temperature. Whitaker (24) stated that in the egg of 

 the brown alga, Fucus, the differentiation is clearly influenced by en- 

 vironmental factors before the first nuclear division occurs. Thus, 

 gradients of visible light, ultraviolet radiation, metabolic products, 

 hydrogen ions, and temperature are capable of determining polarity of 

 an egg ; even mechanical elongation of the egg influences its polarity. 

 In addition, since the protoplasm consists of thread-like protein mole- 



