480 Prof. S. Apdthy on 



The further ontogeny of Salinella also, subsequent to the 

 ah'eady active unicennlar stage, exhibits nothing extraordi- 

 nary, Frenzel writes : — " For it is precisely the further 

 development of this larva, incomplete though my study of it 

 was, which proves that it does not develop into the perfect 

 animal by means of ordinary division, much as a colony is 

 formed from a single Choanoflagellate, but by a far more 

 complicated process, which we may most fitly term endo- 

 genous cell-formation." We may, however, designate the 

 segmentation of all Metazoa whatever, and even the formation 

 of the daughter-colonies of the Volvocinea3, as endogenous 

 cell-division ("cell-formation"). In very many cases the 

 egg-cell has a distinct cell-membrane, and the processes of 

 fission, in which segmentation consists, always proceed 

 within this membrane; it often happens that it is only the 

 already tolerably advanced larva or the almost perfect animal 

 that leaves the cell-membrane of the parent-cell, the egg-cell. 

 Even more distinct endogenous cell-division than in the case 

 of the holoblastic ova is the segmentation in the meroblastic 

 eggs, where, as for instance in the e^g^ of the fly, the limits 

 of the daughter-cells within the cell-niembrane of the parent- 

 cell are for a long time absolutely indistinguishable from one 

 another. 



It is indeed in the chief degree the circumstance that the 

 daughter-cells remain in organic connexion with one another, 

 and that they have no longer the strength to separate, which 

 has replaced societies of cells by the higher category of 

 colonies ; and a still more intimate union of the cells, in 

 connexion with their endogenous origin in the egg-cell and 

 in consequence of their further individual debilitation, 

 characterizes the Metazoa, and makes of them a single indi- 

 vidual, an indivisible physiological whole. 



That the daughter-cells and subsequent descendants of the 

 Metazoon egg-cell have now no longer the power to separate 

 from one another, and lead an independent cell-life like Pro- 

 tozoa or like the unicellular ancestors of the species, is a fact. 

 It remains to be asked, what is the cause of this? It cannot 

 be a change of habit owing to the living together for so long 

 in the cell- colonies of the ancestors, for the latter is itself the 

 first consequence of the cause for which we are seeking. I 

 consider that the cause is to be found in a certain debilitation 

 of the genus of Protoblasts with which we have to deal ; and 

 the latter is again nothing more than the consequence of that 

 change in all protoj)lasms (vital qualities) which sets in as 

 time goes on, even without special external influences, and 

 which we are only able to detect through its combined effect 



