Frenzel’s Mesozoon Salinella. 479 
(like, e. g., Pandorina), but TWO ENTIRE ANIMALS become 
fused together and form a common cyst. Unfortunately 
Frenzel was unable to trace the further phenomena within the 
cyst. It is, however, hardly possible to imagine anything 
else than the fusion of each pair of cells of different origin. 
Tf, as Frenzel writes, a continuation of cell-multiplication 
really takes place within the cyst, this in all probability 
happens before the copulation of the several cells. Unfor- 
tunately, too, Frenzel did not directly observe that the sepa- 
rate similar cells in the cyst pass into the unicellular Ciliate 
form which he has described. 
Should that Infusorian really be a developmental stage of 
Salinella, it cannot nevertheless, as has already been stated, 
be termed a larva. The ova of many other animals also are 
capable of movements, particularly amoeboid ones, and of 
feeding in the INTRACELLULAR fashion upon the neighbouring. 
cells, such as is the case, among others, in Tubularia and 
Hydra; and not only can this be done by the unfertilized, 
immature, reproductive cell, but also, as is well known, by 
the fertilized one, as, for instance, in the case of certain 
Platyhelminthes, where, in addition to a larger number of 
yolk-cells, only a few fertilized ege-cells are found in the 
egg-capsule. The sole difference between Salinella and the 
other known cases of active egg-cells is that the latter have 
only to incorporate and digest the nutritive material which is 
already stored up for them; while on the other hand the 
fertilized ovum (or zygospore) of Salinella has itself to acquire 
its food by its own activity, in order to be able to proceed 
with the building-up of its body. Therefore it is that 
the faculty of reproducing the organization of the highest 
unicellular ancestral form in the highest unicellular stage 
of Salinella does not, as is the case in the majority of 
ova, remain virtual and latent. The necessity of accumu- 
lating the building-material for further development by its 
own activity only sets in in the case of Salinella earlier 
than in that of all other multicellular animals. In point of 
fact much more is demanded from an independent cell in 
Salinella than in higher animals, where the separate cells 
always retain less of the activity and independent energy of 
their unicellular ancestors. For the rest, however, the tran- 
sition from the “cell with intra-cellular digestion to the adult 
animal with extra-cellular digestion ” in the case of Salinella 
is by no means more enigmatical and unexplained than the 
fact that from egg-cells with amoeboid digestion Metazoa 
develop whose body-cells—partly indeed themselves digest 
throughout life—for the greater part, however, are endowed 
with extra-cellular digestion or none at all. 
