468 Prof. S. Apdthy on 



upon the paucity of our supply of facts ; it is, however, on 

 the other hand merely a matter of arbitrary valuation : essen- 

 tially it makes no difference whether an abyss, which we 

 cannot cross, is ten metres or a hundred metres wide. A 

 difference is a difference, and can really be neither greater nor 

 smaller than any other. 



And wherefore must we exclude the Protozoa '' from 

 Plackel's fundamental principle of biogenesis " ? To what 

 extent is our knowledge of the Protozoa to upset this principle ? 

 For if there really are living creatures which are to be 

 EXCLUDED from the fundamental principle of biogenesis, the 

 latter is entirely invalidated. But has it recently been 

 proved that we are confronted with insuperable difSculties if 

 we assume that, in the case of the Protozoa also, ontogeny 

 recapitulates phylogeny ? It is true that the number of dis- 

 tinguishable conditions of form through which the individual 

 life of a unicellular animal passes is much smaller than that 

 of the series of forms in its phylogeny must have been. Yet 

 we see the same abbreviation — relatively still more — among 

 the Metazoa also, and, just as in the Metazoa, the series of 

 forms in the Protozoa often becomes somewhat more complete 

 only in a cycle of several generations. In the same way 

 larval adaptations and other ccenogenetic conditions of form 

 must play a perhaps even greater part among the Protozoa 

 than they do in the case of the Metazoa. 



If phylogeny is really repeated in ontogeny it must be 

 possible to rediscover in the individual development of a 

 Protozoon the initial stage also of the non-nucleate 

 Peotoblast, the stage of the Monera. The same 

 demand must, however, be presented to the Metazoa also ; for 

 in their case, too, phylogeny cannot have proceeded from the 

 nucleate Protoblast, but rather from the non-nucleate primary 

 stage of all living forms. But the ontogeny of every Meta- 

 zoon has hitherto appeared to commence with the stage of the 

 egg-cell (or the reproductive cell in general), therefore with 

 the nucleate Protoblast. Yet I now find it possible, owing 

 to the discovery of the general diffusion of centrosomes 

 (attraction-spheres) and their, so to speak, leading role in 

 cell-division, to trace back the ontogeny of the egg-cell also, 

 and consequently that of all Protozoa, to the stage of the 

 Monera. l3ut the stage of the non-nucleate Protoblasts is 

 at the present time always passed within the mother-cell, 

 before delimitation of the daughter-cells occurs ; for as soon as 

 division has taken place in the centrosoma, the attracted area 

 of which is equivalent to the unit of the Protoblast, therefore 

 to its individuality, the parent individual has ceased to exist; 



