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the union of the protoplasm, we must expect on the' evolution theory 
an incipient stage in which only the latter phenomenon should 
occur. That the nucleus is not invariable, much less indispensable, 
is of course evidenced by the existence of the Monera, or if their dis- 
tinctness he questioned, we may appeal to the recent demonstration, 
apparently by the most refined histological appliances, that in young 
Actinophrys a nucleus is really absent,"^ and develops independently 
in adult life. Moreover, on the present view of the almost primordial 
nature of the Myxomycetes, their plasmodium is the only phenomenon 
which at all resembles conjugation, and since we have already viewed 
amoeboid, ciliated, and resting forms as specialisations of the cor- 
responding phases, it is no great extension of the theory to view 
conjugation as specialised from the plasmodial phase. This view 
will he strengthened when in the, next paper we leave the cell-cycle 
to consider the physiological processes in the protoplasm itself. 
12. Relation between Normal and Pathological Tissues . — Unless 
the step taken by Goodsir and Virchow — of regarding all patho- 
logical variations as ultimately expressible in terms of cellular 
structure and function, ^.e., of the cell theory, be deliberately re- 
traced, we cannot avoid the application of the present re-statement of 
the cell theory to pathology. To do this in detail would, of course, 
require far more than the writer’s knowledge, but a few brief and 
tentative suggestions may be put forward. Pathologists are reducing 
tumours to a common type — which seems essentially that of cell 
multiplication in the resting or encysted stage. It is certainly more 
easy to suppose, on the present view, that the appearance of a con- 
nective tissue tumour has been due to the placing of ordinary cells 
in new conditions favourable to the assumption of that phase of the 
ancestral cycle ; or from a slightly different point of view, to say that 
that inhibition of the cycle essential to the permanence of the whole 
organism has been locally removed, than, for instance, to suppose, with 
Cohnheim, the existence of a long dormant mass of embryonic tissue. 
Again, we can easily modify the environment of living cells under 
the microscope^ — we can accelerate or diminish the activities of 
ciliated epithelium, by heat and cold, oxygen and carbonic acid, 
by alkali and chloroform. I have elsewhere f pointed out that the 
* Gruber, Zool. Anzeiger, No. 118, 1882. 
t Op. cit., Proc. Roy. Soc. Loud., 1879. 
