M. J. Frenzel on the Mesozoon Salinella. 81 
rather regard absorption in the Metazoa as a purely chemical 
process, emanating from the living cells. 
Now, should we desire to construct a multicellular animal 
from a number of Protozoa, e.g. from Ciliate Infusoria, we 
should consequently soon be confronted with a great physio- 
logical difficulty. Wecould indeed easily imitate the simplest 
Metazoon type, and so arrange the cells that they should 
surround a cavity possessing an incurrent opening. But 
how would nutrition proceed? The group of Protozoa would 
at all events obtain their food from the common cavity, but 
it would be directly introduced into the interior of the separate 
individuals, there digested, and so forth. It follows that in 
this construction of ours we should not get beyond a simple 
Protozoon colony, and should still be a long way from 
‘obtaining a typical Metazoon. For although among the 
Metazoa there are forms which possess intracellular digestion, 
we must nevertheless not forget that it is only the endoderm 
cells which can be concerned therein. But yet all the other 
tissues must be similarly nourished, and this is effected by 
their receiving already digested matters from the intestinal 
cells. Were we able therefore still to regard the latter at all 
events as Protozoon cells, this view would be absolutely 
inadmissible for the former, the cells of the mesoderm and 
ectoderm, and they must absorb in a manner similar to that 
of the intestinal cells which possess the power of extra- 
cellular digestion. 
From the foregoing considerations it is not difficult to see 
that the multilamellar character of the Metazoa in itself entails 
the decisive difference which separates them from the Proto- 
zoa, and, further, that the multicellular character, as such, is 
insufficient to bridge over the deep gulf between the two 
principal groups of the animal kingdom. 
It is well known that the title Mesozoa has already been 
bestowed upon organisms which it must be confessed are 
strange enough, and which rendered the justification of the 
term not improbable. But the position of the Orthonectids 
and Dicyemids is nevertheless an extremely doubtful one, 
and points more to an affinity with the worms. The genus 
Trichoplax, moreover, has been with good reason assigned to 
the Metazoa by Fr. Schulze; for although its conditions of 
nutrition may be regarded as being still very obscure, never- 
theless it has not been possible to determine that its digestive 
processes are intracellular. 
It thus came to pass that the group Mesozoa once more 
disappeared from the scene. I therefore consider that I am 
entitled to regard the chance as a lucky one which enabled me 
Ann. & Mag. N. Hist. Ser. 6. Vol. ix. 6 
