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of Linnseus, and the numberless anatomical resemblances and differ- 
ences investigated by Cuvier and his disciples, become reduced to 
resemblances and differences in the details of structure and position 
of fundamentally similar unit masses ; while the resemblances of 
development made known by embryologists become the connecting 
link between the cell theory and these generalisations of adult 
structure. It is not necessary to do more than merely allude to 
such applications of the cell theory, or to that of the study of patho- 
logical structure initiated by Goodsir and Virchow, or to that 
brilliant confirmation of the unity of the animal and vegetable cell 
which has lately been afforded by the detailed study of the processes 
of cell multiplication. Agassiz* was fully justified in the opinion 
that the most brilliant result of modern science was the ovum-theory, 
and thus it is beyond dispute that “ in our own day, as in those 
of Bichat and Schwann, the labours of the histologist, when inspired 
by higher aims than that of the mere multiplication of descriptive 
detail, are of supreme morphological importance, and result in the 
demonstration of a unity of organic structure deeper even than any 
which we owe to Linnseus or Cuvier, Goethe or Geoffroy.” f 
Cell — The position and importance of the cell theory being thus 
defined, the fundamental necessity for a precise conception of the 
cell itself will be sufficiently obvious. The early progress of this is 
well known ; at first the vegetable cell-wall gave the type, while 
Schwann’s cells were essentially nucleated vesicles with fluid con- 
tents. Dujardin described the sarcode ” of Foraminifera ; Von 
Mohl discovered the “ protoplasm ” of the vegetable cell ; while Max 
Schultze identified both as the same substance; showed it, and not 
the membrane to be essential ; and gave an amended definition of 
the cell as a unit mass of nucleated protoplasm. For working 
purposes it is this conception which is generally accepted, and 
almost every dissertation or treatise upon the general questions of 
botany or zoology, histology or physiology, commences by postulat- 
ing it, the amoeba being most frequently taken as the standard type. J 
Unsolved Problems . — Such a conception of the fundamental 
* Essay on Classification. 
t “Morphology,” Ency. Brit., xvi. sec. 3, p. 840. 
% Of this no better instance can be afforded than the introduction to the 
admirable Manual of Physiology of Dr Michael Foster. 
