CHAPTER IV 



ON THE RELATION BETWEEN THE INVERSION OF 



SPIRALLY TWISTED ORGANISMS AND THE 



MOLECULAR INVERSION OF THEIR 



PROTOPLASMIC CONSTITUENTS 



1. Morphological Dissymmetry and Morphological In- 

 version. The attention of biologists has for a long time 

 been attracted by the existence of dextral and sinistral 

 spirally twisted forms in some animal or plant popula- 

 tions. Ludwig (1932, 1936) published two extensive re- 

 views in which he summarized a large number of scattered 

 observations on this subject. These reviews show that 

 practically all the studies of dextrality and sinistrality in 

 plants and animals consist in descriptions of the morpho- 

 logical aspects of the phenomenon and that the physio- 

 logical mechanism which underlies the morphological 

 processes has been left almost untouched. 



One of the basic attributes of spiral structures is their 

 ability to undergo genotypic inversion. The work of 

 Boycott, Diver, Hardy and Turner (1929) on the heredity 

 of sinistrality in the mollusc Limnaea peregra has shown 

 that the usual twist of the coil of this mollusc to the 

 right (clockwise) is determined by a dominant gene, while 

 the twist to the left is controlled by the recessive gene, 

 and that the sinistral mutant individuals appear in the 

 population from time to time. Consequently, in almost 

 all the cases in which some experimental work was car- 

 ried out with organisms possessing a spiral form, it 

 was possible to detect among the usual, typical individ- 

 uals a few hereditary inverse specimens. (We shall, 



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