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

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158 GILBERT 0. BOURNE. are several Ciliata which have as many as one hundred nuclei, e.g. Holophrya oblonga, Lagynus elongatus, and Uroleptus roacovianus. 1 I do not include as multinuclear thoseformsinwhich,asiuTrachelocerca phoeni copter us or Chcenia teres, the chromatin is scattered throughouttheprotoplasm in the form of minute granules. Those Protozoa only may be considered multinucleate in which there are several welldefined aggregations of chromatin. And even if the Ciliata above mentioned may not be considered truly multinucleate, but to possess onlya fragmented nucleus,there can be no doubtabout some Amoebae, e.g. Amoeba quarta and others described by Gruber. 2 In the last-named the multinuclear state is constant ; as Gruber says, " es sich nicht etwa urn vorubergehende Entwicklungszustande handelt." He watched these Amoebae for a long period, expecting that the large number of nuclei would at last find its explanation in reproduction by multiple fission, but he was unable to observe any such culmination. Dr. Gruber is a great authority, and he, equally with Zeller and others, is quite positive that the multinuclear Protozoa are truly unicellular. His reasons are, that closely allied species are uninuclear, and that the protoplasmic body is continuous—contained in the case of Ciliata by a single cuticular coat. But even he admits that the only reasonable interpretation of the multinuclear condition is that it is a prelude to reproduction, that is, to cell division. 3 It is, therefore, a condition intermediate between the unicellular and the multicellular condition, or, as I should like to call it, a hypopolycytial condition, and nothing more need be affirmed of it. Zeller is quite precise as to his reasons for regarding Opalina as unicellular. " Die kleinsten. Thierchen aller bekannten Opalinen, so wie sie von Neuem sich zu entwickeln beginnen, besitzen nur einen einfachen Kern und entsprechen 1 Maupas, "Etudes des Infusoires cilies," 'Arch. Zool. exper. et gen.' (2), i, 1883. 2 ' Zeit. fur wiss. Zool.,' xli, p. 186. ' Aug. Gruber, "Ueber vielkernige Protozoa," 'Biol. Centralblatt,' iv, p. 710.
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
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