57 



V 



tible with the real character of symmetry, than motion is. For that 

 reason the organs of plants are, as a whole, arranged with Jiigher 

 symmetry, and they are also more symjnetrical in themselves than 

 those of the animals; while the most(^per feet) symmetry finally is 

 manifested in the forms of immobile, crystallised matter. On the other 

 hand, for the animals which can move freely, the best mechanical 

 stability may have been a factor of importance in the development 

 of their somatic forms. l ) 



By the investigations of Przibram, Loeb, and others, the atten- 

 tion of experimental biologists has also been drawn to the special 

 significance of the bilateral symmetry in somatic forms for the expla- 

 nation of certain classes of dynamical phenomena in biology. 2 ) Thus, 

 in numerous cases, the natural bilateral symmetry of the organism, 

 disturbed by accidental or intentional injury or by amputation 

 of certain organs, automatically reappears, and in many cases even 

 at the cost of the normal development or by degeneration of the 

 other organ yet present. All phenomena observed are evidently 

 aimed at the preservation of the existent symmetry in the organism, 

 which itself is determined as an union of two symmetrical and 

 mutually independent halfs of its body. 



Something analogous occurs with respect to the reaction of living 

 organisms upon unsymmetrically applied stimuli, as observed in 

 cases of phototropism (plants; Eudendrium, starfishes, etc.), of eo- 

 tropism, of chemotropism, etc. The automatical and irresistible move- 

 ments performed by the individuals in such cases, always point to 

 a special orientation of it with respect to the direction of the stimu- 

 lating influence. According to Loeb's ideas, all such kinds of 

 "tropism" should be considered as the direct results of certain 

 functional dissymmetries, and as aimed at the restoration of definite 

 conditions of symmetry. 



7. Proceeding with the deduction of the possible groups of the 

 second order, we can now start with those groups C n of the first 

 order dealt with in the previous chapter, which only possess a 

 single heteropolar axis of the first order, and combine these groups 

 C n with a typical symmetry-element of the second order in the way 

 formerly discussed. 



2 ) Cf. : F. M. Jaeger, Over Kristallografische en Molekulaire Symmetric van 

 plaatsings-isomere Benzolderivaten, Dissertatie Leiden, (1903), p. 202 208; Zeits. 

 f. Kryst. 38, 592, (1904). 



3 ) J. Loeb, "Dynamik der Lebenserscheinungen" , Leipzig, (1906). 



