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are essentially those ‘variations which happen not to be conducive to 
success in the struggle for existence, and all variations normal and 
pathological alike are ultimately cellular. The structural and functio- 
nal aspects of the theory are here again available, the former yields us 
a means of classifying the normal and pathological variations of struc- 
ture alike, the functional aspect of interpreting them, both of course 
in terms of »the cell cycle«. Pathologists are reducing tumours to a com- 
mon type essentially that of cell multiplication in the resting stage, 
the formation of pus and perhaps disorders of the ciliary epithelia are 
degenerations to the amoeboid stage, while inflammatory changes may 
be interpreted as a temporary and excessive intensification of cell acti- 
vity. 
U. An Hypothesis of Cell-Structure and Contractility. 
The amount of attention which has recently been paid to the in- 
ternal structure of the cell has not as yet resulted in the establishment 
of any sufficiently comprehensive generalisation, and an hypothesis 
which attempts at once to unify the numerous hitherto uncoordinated 
observations as well as to throw light upon that theory of the cell cycle 
of which an outline has above been propounded, may be at least sug- 
gestive if not completely exhaustive. Let us survey a few of the main 
differences in protoplasmic structure which any such hypothesis must 
aim at unifying. 
While the lowest amoeboid forms are simply granular, others are 
distinctly differentiated into clear ectoplasm and granular endoplasm. 
The immense variability of the size, form and general appearance 
among the Rhizopods has not been sufficiently allowed for, so that 
there is every reason for doubting, whether the vast majority of de- 
scribed species have any real distinctness. The elongated and reticu- 
lated, granular and circulating pseudopodia of the Foraminifera, or the 
radiating, clear, and scarcely contractile pseudopodia of a Heliozoon are 
however sufficiently characteristic and must be reckoned as fairly di- 
stinct differentiations of protoplasm. The remarkable changes visible 
in ova before and during fertilisation, the stroma of cells and the phe- 
nomena exhibited during cell-division require to be accounted for. 
Such an hypothesis too should aim at throwing light on the mystery of 
muscular structure and should deal even with such apparently peculiar 
phenomena as that aggregation of protoplasm described by Darwin as 
occurring in the cells of insectivorous plants, which when in active 
nutrition or when subjected to chemical, electrical and mechanical sti- 
muli, exhibit the protoplasm aggregated into two portions — the outer 
more or less hyaline but containing irregular and constantly changing 
