472 Prof. S. Apdthy on 



is not one of tliose who are at once inclined to regard every 

 reflection against their train of thought as " an attempt to 

 pick holes " (" Anbohrungen "). 



In his article Frenzel lays most stress upon the supposed 

 gulf between Protozoa and Metazoa, which is stated to be 

 caused by the fact that the digestion of the Protozoon cell is 

 intra-cellular, while among the ^letazoa, on the contrary, 

 where extra-cellular digestion prevails, the intra-cellular mode 

 " is only met with in isolated and exceptional cases." In 

 opposition to this I consider — and in so doing I am supported 

 by the leading existing authorities — that the way in which 

 the cell feeds in the Protozoa and Metazoa is least of all 

 adapted to form a gulf between them. Quite on the contrary ! 



Among the Protozoa it may be a matter of momentary 

 adaptation whether the digestion of one and the same animal 

 is extra- or intra-cellular. And among the Metazoa intra- 

 cellular digestion is not only not of isolated occurrence, but in 

 the whole of the lower forms is, so to speak, predominant ; in 

 many, as e. g. in the Sponges, such a digestion is perhaps 

 exclusively present. Moreover it is not " only the endoderm 

 cells which can be concerned therein ; " but also, and indeed 

 chiefly, the amaboid cells of the mesenchyma, which, even in 

 the highest Metazoa, as so-called phagocytes, continue to 

 practise this faculty of theirs which they have retained from 

 the Protozoon stage. Should we desire to construct a Meta- 

 zoon out of Protozoa, we should not find, as Frenzel believes, 

 any physiological difficulty at all in the mode of nutrition. 

 Since the several individuals in the colony also would each 

 digest for itself by the intra-cellular method, we could per- 

 fectly well get " beyond a simple Protozoon colony " and 

 obtain a " typical Metazoon." If we take into consideration 

 the more recent facts of comparative embryology and ])hysio- 

 logy among the lowest Metazoa, we arrive at the result that 

 the several cell-individuals of the Metazoon, which continually 

 relinquish more and more of their independence (in ray 

 opinion because the rate of Protoblasts which is represented 

 by them continually forfeits more and more of its vital 

 energy), have on that account long retained the faculty of 

 digesting their food for themselves. It is })robable that this 

 faculty was first lost in the ectoderm cells and then in those 

 of the endoderm, while, on the contrary, the cells of the 

 mesenchyma, even in the highest forms, are to-day still able 

 to digest for themselves. 



In opposition to Frenzel, we must entirely agree with 

 Metschnikotf " that this mode of digestion represents one of 

 the few properties of the Metazoon organism which have 



