44 



Fig. i. 



Fig. 2. 



Probable course of development of 

 the dark variant by direct heterogene 

 cell-partition or evolution. The first 

 partition produces from the single lu- 

 minous bacillus one of the same, and 

 another of lessened luminosity. The 

 second partition produces from the 

 latter again one of the same lumi- 

 nosity, and another quite-dark. 



Less probable course of development 

 of variant by indirect heterogene cell- 

 partition or epigenesis. 



Fig. 3- 



Fig. 4. 



Fig. 5- 



Pedigree of Ph. indicum, 

 normal form. 



Pedigree of parvum. 



' -L. 



I .-.""" 



Pedigree of variable 

 obscurmn. 



If the normal form is indicated by , the obscurum-variant by , and the par- 

 fw-variant by -J-, unreckoned the sub-variants, the pedigree of the normal form of 

 Ph. indicum can be represented by Fig. 3, which means, that at the two first re-in- 

 oculations only the normal form is produced, and that at the third likewise obscurum- 

 and />arz'm-variants have orginated, but from cells which were subjected to particular 

 conditions. The numbers 2 and 3 for the generations are chosen arbitrarily, for the 

 number of generations, after which the variation occurs, can be regulated at will, for 

 by early re-inoculating the young cultures on fish-broth-agar (not on fish-broth- 

 gelatin) the variation can be kept back for a long time x ). 



For the variant par-vum the pedigree becomes somewhat different from that of 

 the normal form, there being much atavism (Fig. 4). 



The pedigree of obscurum can, as to the constant form, be represented by a 

 single mark. 



The variable, obscurum, again produces atavists, but less than parrum, and 

 besides ^art'Mw-variants (Fig. 5). 



In these three last schemes are, as said, the sub-variants left out. 



I have not succeeded from Ph. indicum to obtain a perfectly constant luminous 

 form, that is, one which produces no variants, though I have tried for years to do this 

 by selection. It is evident that the conditions of culture inavoidably give cause to 

 the rise of variants. That for the rest the faculty of varying in a very determined 

 way, is deeply rooted in the nature of the cell, is proved by the following observations. 



To these relations I hope to refer at another occasion. 



