Raymond Pearl 
271 
expect that there would be absohitely more variation in the non-conjugant type 
than in the conjugant, because the non-conjugant individuals are larger, but if we 
take the variation in proportion to the mean size of the conjugant and non- 
conjugant groups wc obtain the same result. 
Thus : 
Coefficient of variation of conjugant means = 2"586 7^. 
Coefficient of variation of non-conjugant means = 5"174 . 
The general conclusion which we reach is that, su far as can he judged bij the 
data at present available, the conjugant type is relatively much more constant as -we 
2)ass from adture to culture than is the non-conjugant type. Of course our present 
data are much too meagre to demonstrate this conclusion. It is true for the 
material here studied : whether it is true generally can only be determined by 
further investigation ; but the present results certainly give a fair degree of 
probability that it is generally true. 
To recapitulate then the results of this investigation show that in the material 
studied (a) there is a differentiated "conjugant type" of Paramecium, and (h) this 
" conjugant type " is relatively fixed and constant under varying environmental 
conditions, as compared with the type of the general population in fission generations. 
Now I take it to be a well-established result of the work of Calkins and earlier 
investigators in this field that (c) at more or less regular intervals in the normal 
life history of a race of Paramecium the individuals which are to take part in 
the future propagation of the race not only do, but under normal conditions must 
pass through a period of conjugation. Otherwise the race will die out. Calkins' 
brilliant studies {loc. cit.) have shown that for a time the race may be kept going 
by various forms of artificial stimulation, but that in the end such stimulation 
fails in its purpose. But if these three conclusions, {a), (b), and (c), «re true, tJien 
it clearly means tliat those individuals winch take part in the perpetuation^ of the 
■race conform at intervals to a definite and relatively fixed morphological type. This 
result I believe to be of considerable importance, for, if it be accepted, it seems 
to me to mean nothing less than that we must change somewhat radically our 
whole outlook on the relation of the Protozoa to evolution problems. It has 
been held as axiomatic in biology that acquired characters are inherited in the 
Protozoa because one cell is both soma and germ. But clearly it matters very 
little to the race whether acquired characters are inherited or not, if after every 
cycle of fission generations the organism must come back to the same type (barring 
any real evolutionary change which may have taken place) that it started from, 
or in the end die. The case then becomes not very nruch different from what 
obtains in higher organisms. In the Metazoa what is acquired by the soma in 
one generation is not usually, at least, passed on to the next. Real evolutionary 
progress depends on changes in the germ cells. But similarly, if what we have 
concluded for Paramecium be correct: All real evolutionary progress in such a 
jyrotozoan form must consist in definite changes in tJie "conjugant type." So far as 
evolutionary progress is concerned the conjugant individuals in the Protozoa 
