47 



That many so-called new species will prove only variants of other species and 

 no good species, is not improbable. Especially in the microbes, where the want of 

 crossing must strongly favour the prolonged continuing of the once formed variants, 

 it is to be foreseen that in nature will often be found variants, which will long main- 

 tain themselves at their habitat. If they are isolated, the discoverer will at first be 

 almost sure to see new species in them, and only after an accurate investigation 

 recognise them as variants of another species. 



The sub-variants of the microbes prove, that the characteristics which in the 

 main variants are quite wanting disappear by little leaps from the normal forms. In 

 other cases, however, the main variants seem to appear suddenly, whence it would 

 follow, that a characteristic can also vanish at a single leap at the cell-partition; but 

 here the sub-variants may have escaped from observation. 



The variants of the microbes, regarded as cell-variants, prove that out of a cell 

 daughter-cells may spring unlike to the mother-cell. Though the way in which this 

 is effected is still insufficiently known, it proves the existence of heterogene cell- 

 formation, whether by direct heterogene cell-partition (fig. i), or, by the less prob- 

 able transformation (fig. 2). 



In order to show how decidedly heterogene cell-formation is still considered as 

 impossible, so that it is not superfluous to afford a new evidence for its existence, I 

 refer to the well-known book of O. H e r t w i g Die Zelle und die Gewebe, p. 64, 

 Bd. 2, Ed. 1898, where we read as follows: Die Theorie der heterogenen Zeugung, 

 wo sie aufgestellt wurde, ist als grober Irrthum bald beseitigt worden. So gilt als ein 

 allgemeines Grundgesetz in der Biologic der Ausspruch Gleiches erzeugt nur 

 Gleiches oder besser Art erzeugt stets seine Art. Bei alien einzelligen Lebewesen 

 ist erbgleiche Theilung ihres Zellenorganismus die einzige, die vorkommt und vorkom- 

 men kann. Auf ihr beruht die Constanz der Art. Wenn es moglich ware, dass bei 

 irgend einem einzelligen Organismus die Erbmasse (Idioplasma) durch Theilung in 

 zwei ungleiche Componenten zerlegt und auf die Tochterzellen ungleich iibertragen 

 werden konnte, dann hatten wir den Fall einer heterogenen Zeugung, den Fall der 

 Entstehung zweier neuer Arten aus einer Art. Wie indessen alle Beobachtungen 

 lehren, werden auch bei den Einzelligen die Arteigenschaften so streng und bis ins 

 Kleinste iiberliefert, dass einzellige Pilze, Algen, Infusorien auch noch im millionsten 

 Gliede, ihren weit entfernten Vorfahren genau gleichen. Der Theilungsprocess als 

 solcher erscheint daher auch bei den einzelligen Organismen nie und nirgends als 

 Mittel um neue Arten ins Leben zu rufen. 



The preceding pages prove that this view is erroneous, so that the far reaching 

 conclusions, drawn from it in relation to ontogeny vanish at the same time. 



So far there is thus no reason in contradiction with observation, which forbids 

 admitting, that the ontogeny of the higher organisms consists in a regular course of 

 variation processes, and that full-grown plants and animals are built up of as many 

 cell-variants of the embryonal cells, as they contain different tissus composed of 

 identic cells. 



