A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...

A CRITICISM OP THE CELL-THEORY. 159
unzweifelhaft, wie Engelmann schon fiir die von ihm untersuchte
Art nachgeweisen hat,' morphologischvollstandigeinereinzigen
Zelle.' Aber auch mit der weiteren Entwicklung andert sich
daran nichts. Mag die Zellhaut zu einer aus vielen einzeln
zerlegbaren Bandern bestehenden muskuloses Hiille 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, 0. obtrigona und 0. dimidiata,
die protoplasmische Korpersubstanz selbst zeigt
keine weitere Veranderung als die der Masseuzunahme
und blebt, wie auch Engelmann hervorhebt,
' Zeitlebens eine einzige zusammenhangender Masse,
•wie von eine einzigen Zelle. 5 " 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 showa no other change than increase
in size, and because it remains, its life long, a single continuous
mass. The same argument leads many to regard the
Coeloblastae 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
Coeloblastae 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 continuous.
The same may be said for muscle cells (Werner and
Klecki), for connective tissue, for bone cells, for the developing
mesoblast of Vertebrata (teste Sedgwick, Assheton, and
others), for the mesoblast (mesenchyme) of trochospheres and
Molluscan larvae (see particularly von Erlanger), and for many
other tissues.
Thus the inevitable result of an argument which is meant