46 



teristic at a time. In the sub-variant one characteristic of the normal form is partly, 

 in the main-variant it is wholly changed. In new varieties and species more charac- 

 teristics are varied. 



Furthermore resuming the above given statements I come to the following con- 

 clusions. The here discussed forms of hereditary variability belong to three types: 

 At degeneration all individuals, by a slow process of variability, lose their vegetative 

 power, so that the species may cease to exist. At transformation, which seems to 

 appear more seldom, all individuals lose a specific characteristic and acquire either 

 or not another instead. At the common hereditary variability or variation, the 

 normal form, probably by heterogene, cell-partition, throws off some individuals, the 

 variants, mostly differing from it by a strongly salient characteristic. The normal 

 form itself propagates beside it quite unchanged. The variants are constant in a way 

 corresponding with independent species, sometimes this constancy is perfect, in other 

 cases atavists are produced, like to the normal form. Subvariants i. e. intermediate 

 forms between normal form and variant, are less found than the variants themselves, 

 but they are perhaps never wanting, and are in the same way constant as. the normal 

 forms. Whether the sub-variants are also originally formed in smaller number than 

 the main variants is uncertain ; what is seen is that they rapidly disappear from the 

 cultures and are supplanted by the normal form and main variants if they are not 

 fixed by colony-selection. Besides, each well-defined degree of variation, however 

 slight, seems to be fixable. 



The rare occurrence of the sub-variants throws some light, First, (by the comparison 

 of the individual microbes with the individuals of the higher organisms) on the 

 marked distinctness by which in higher plants and animals most varieties and species 

 are separated, for they originate by repeated variation processes, relative to 

 different characteristics and the chance that the common and distinctly discernable 

 variants will partake therein and not the rare sub-variants, more difficult to 

 distinguish, is accordingly greatest 1 ). 



Second, (by the comparison of the individual microbes with the tissue-cells of 

 the higher organisms) on the no less marked confines between the tissues and the 

 organs of one and the same individual, for these are constituted of as many cell- 

 variants of the embryonal cells, cell-variants, which will supplant the cell-sub- 

 variants. 



') I perfectly agree with Professor de Vries, that the origin of species should often 

 be sought in the almost suddenly produced variants, or mutants, as he calls them. This 

 is also the conclusion to which Gallon has come regarding the races, and to which 

 he referred repeatedly since 1892, the last time, so far as I know, in Nature T. 58, pag. 

 247, 1898 in these words: I have frequently insisted that these sports or aberrances 

 (if I may coin the word) are notable factors in the evolution of races. Certainly the 

 successive improvements of breeds of domestic animals generally, as in those of horses 

 in particular, usually make fresh starts from decided sports or aberrances aud are by 

 no means always developed slowly through the accumulation of minute and favourable 

 variations during a long succession of generations*. Along quite distinct ways Gallon, 

 de Vries and myself have thus arrived at the same conclusion regarding the probable 

 origin of many races and species. But the great difficulty which lies in the explanation 

 of the adaptions, has not been removed, neither by Gallon's aberrants, de Vries 

 mutants, nor mv variants. 



