An Experimental Study of Somatic Modifications etc. 34 5 
that these warm-room descendants were no smaller than the cold- 
room descendants. Indeed they were larger at the time of the second 
measurements. 
G. One of the alternatives considered above (C) might be offered 
in a modified form. It might be conceded that temperature as such 
could not affect either the fetus or the germ-cells to any appreciable 
extent. But it might, on the other hand, be contended that the effects 
of temperature, even upon the parent body itself, may not be direct, 
but may be due to the formation of specific chemical substances 
which, through the medium of the blood, may be supposed to simul- 
taneously influence the body and the germ-cells. Such a hypothesis 
can neither be proved nor disproved in the present state of our 
knowledge, but it is perhaps the type of explanation which is cal- 
culated to appeal most strongly to the biologist of to day. It may be 
pointed out, however, that if a mechanism exists whereby the germ- 
cells may be so influenced as to bring about a modification of the off- 
spring parallel to that which was undergone by the parent^ such a 
mechanism would be of exactly the same value for evolution as the 
yinheritance of acquired characters <^ in the old sense. For heredity, 
however, the case would be somewhat different. We might still 
continue to talk about the » continuity of the germ-plasm «, though 
that expression would have been shorn of much of its meaning. 
H. Finally, we have the view that the changes undergone by the 
parent body are themselves registered in some way in the germ-cells, 
so as to be repeated, in a certain measure, in the body of the off- 
spring. The » classical « attempt to make this process intelligible is 
of course Darwin's hypothesis of ^pangenesis*. Other views have 
been put forward recently i) which are scarcely to be distinguished 
from the preceding type of explanation (G). 
In conclusion, the writer will express his qualified conviction 
that the truth is contained in one or both of the last two alternatives. 
It would not be profitable, however, to enter into any scholastic dis- 
cussion of these various hypothesis. One after another of these alter- 
natives must be excluded by carefully planned experiments, and it 
is the intention of the present writer to continue such experiments 
on a much greater scale in the near future. 
Naples Zoological Station 2), Feb. 26, 1910. 
1) E. g. the »hormone theory« of Cunningham (Archiv f. Entw.-Mech. 1908 . 
2) My hearty thanks are due to the director and staff of the station for 
facilitating the work of preparing this paper, particularly in placing at my 
