472 Prof. S. Apathy on 
is not one of those 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 Metazoa, 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 é. 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 amceboid 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 physio- 
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 my 
opinion because the race 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 probable 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 
Metschnikoff “that this mode of digestion represents one of 
the few properties of the Metazoon organism which have 
