
INAUGURAL ADDRESS. 13 
draws attention to is the direct action of the environment.* 
He points out very truly that this action is accountable 
for the beginning of that marked difference between the 
outside and the inside of organisms which is almost 
universal, and which we recognise when we speak of the 
ectosare and endosare of a Protozoon, the ectoderm and 
endoderm of the Metazoa, the epiblast and hypoblast 
of embryos, and when we distinguish a skin, integument 
or exoskeleton from the organs beneath. The first formed 
organisms must have been homogeneous protoplasm, and 
the direct action of the environment or external medium, 
by causing the first differentiation between the external 
and the internal layers, and by producing slight differences 
between the individuals was, as Spencer says, the 
primordial factor of organic evolution, and was the cause 
of the first variations without which natural selection 
could not take place. 
Although we may admit the modifying effect of the 
direct action of the environment, still it is exceedingly 
difficult in any particular case to distinguish between the 
result of this action and that of natural selection. A few 
weeks ago, while collecting animals at low tide on the 
west coast of Scotland, I found in a rock pool a peculiarly 
coloured specimen of the common sea-slug Doris tuber- 
culata. It was lying on a mass of volcanic rock (of which 
there was a good deal in the neighbourhood) of a dull green 
colour, partially covered with rounded spreading patches of 
a purplish pink Nullipore, and having numerous whitish 
yellow Spirorbis shells scattered all over it—the general 
effect being a mottled surface of dull green and pink 
peppered over with little round cream-coloured spots. The 
* See also Eimer, ‘‘Die Entstehung der Arten auf Grund von Vererben 
erworbener EHigenschaften nach den Gesetzen organischen Wachsens,” Jena, 
1888. 
