478 Prof. 8. Apathy on 
arrangement of the cells which have wandered into the 
original cavity is also wanting. But so soon as a communi- 
cation was constituted between the cavity of the Blastula and 
the exterior by means of a mouth-opening, there was also 
provided the incentive for the immigrant cells to arrange 
themselves again like an epithelium, this time as an endo- 
derm, and to pass from the Gymnomyxa form into a Corti- 
cata phase once more. Thus we already have the true 
Metazoon, a Ccelenterate, or one of the Porifera before us. 
In this series of stages we nowhere miss the Gastrea. 
A greater difficulty than those advanced by Frenzel appears 
to me to consist in the fact that it is not easy to form an idea 
as to how the single individuality of the Metazoon has arisen 
from the separate individualities of the Protozoa, which at 
first composed a loose colony as ancestral form. ‘This, how- 
ever, is at once a question which directly touches upon the 
relationship between the soul of the Protozoa and that of the 
Metazoa, that is really the question of the soul in general! 
Frenzel finally observes something also in the development 
of Salinella which is said to be difficult to harmonize with 
our previous knowledge. He speaks of a hypotrichous Infu- 
sorian-like unicellular animal, which he regards as the LARVAL 
STAGE of Salinella. ‘“ This nevertheless leaves a difficulty of 
considerable importance to be surmounted,” he adds, “in that 
the transition from the single cell with intra-cellular diges- 
tion to the adult animal with extra-cellular digestion is enig- 
matical and completely unexplained.” I would not consider 
this phenomenon to be so very enigmatical, even should the 
fact be established that the digestion of Salinedla is really 
enzymatic, and not intra-cellular, like that of the majority of 
the lower Metazoa. This point, however, has already been 
sufficiently disposed of. Let us at once proceed to consider 
WHETHER A UNICELLULAR ANIMAL, WHATEVER ITS STRUCTURE, 
can be considered AS THE LARVA OF A MULTICELLULAR FORM. 
That stage in the ontogeny of the multicellular animal 
which, while still unicellular, immediately precedes the multi- 
cellular condition, and is therefore the highest unicellular stage, 
we term, whether fertilized or unfertilized, the ripe EGG-CELL. 
In the case of Salinella we have before us—if I rightly com- 
prehend the meaning of a phenomenon observed by Frenzel— 
the product of an act of copulation, we might say a zygo- 
spore; there can in this case be no question of an actual 
ege-cell, for there is no difference to be observed between the 
two copulating cells, and in fact in Salinella there are no 
special reproductive cells at all. All the cells in the body 
have the power of multiplying the species, and, singularly 
enough, the colony does not first relapse into its constituents 
