A CRITICISM OF THE CHELL-THEORY. 159 
unzweifelhaft, wie Engelmann schon fir die von ihm untersuchte 
Art nachgeweisen hat, ‘ morphologisch vollstandig einer einzigen 
Zelle.’ Aber auch mit der weiteren Entwicklung andert sich 
daran nichts. Mag die Zellhaut zu einer aus vielen einzeln 
zerlegbaren Bandern bestehenden muskuldses Hille werden 
und mag der Kern in zwei Kerne zerfallen, wie in O. similis 
und O. caudata, oder durch fortgestzte Theilungen eine 
schliesslich sehr grosse Menge von Kernen aus sich hervorgehen 
lassen, wie in O. ranarum, O. obtrigona und O. dimidiata, 
die protoplasmische Korpersubstanz selbst zeigt 
keine weitere Verinderung als die der Massen- 
zunahme und blebt, wie auch Engelmann hervorhebt, 
‘Zeitlebens eine einzige zusammenhingender Masse, 
wie von eine einzigen Zelle.’” I have put the last passage 
in italics, because it expresses most clearly why Zeller and other 
authors regard multinucleate forms as unicellular, namely 
because the protoplasm shows no other change than increase 
in size, and because it remains, its life long, a single con- 
tinuous mass. The same argument leads many to regard the 
Ceeloblastz as unicellular. The continuity of the protoplasm, 
then, is the test of unicellularity. 
If anybody accepts this, he cannot escape from its logical 
consequences. Not only are multinucleate Protozoa and 
Ceeloblastz unicellular, but also the whole kingdom of plants, 
for their protoplasm is continuous: the developing Peripatus 
is unicellular, for its protoplasm is continuous ; the epithelial 
cells of many animals, as Max Schulze, Pfitzner, Klein, 
Paulicki, Th. Cohn, and others have shown, are united by fine 
protoplasmic processes much as are the cells of plants, therefore 
the epithelia are unicellular, for their protoplasm is continu- 
ous. The same may be said for muscle cells (Werner and 
Klecki), for connective tissue, for bone cells, for the developing 
meseblast of Vertebrata (teste Sedgwick, Assheton, and 
others), for the mesoblast (mesenchyme) of trochospheres and 
Molluscan larve (see particularly von Erlanger), and for many 
other tissues. 
Thus the inevitable result of an argument which is meant 
