90 The American (icoloiiist. i-.'bniiu-y. looi. 
along the Cambrian beach Hne, and we are led to accept for 
them an annelidan origin. It is, as we pass upward geologically 
in the inspection of these classified fossils of the Hall collec- 
tion that we meet, in the deeper seas of the Calciferous group, 
a development of sisc and skeletal mass in the heavy shelled 
brachiopods, gasteropods and cephalopods. 
If the acquirement of hard parts by the shore fauna was 
due to the siccative influences of their position, their response 
to light stimuli, and their gradual assumption of protective coats 
against the violence of waves, the more robust and calcareous 
groups which succeed them may be related to water pressure 
and the bountiful supplies of dissolved mineral elements in the 
deeper seas. I do not know where to turn for evidence on this 
point. Barotaxis has been by Verworn distinctly indicated as a 
physiological agent. "Every degree of pressure can act as a 
stimulus, from crushing or cutting, which destroys the con- 
tinuity of the substance, down to the slightest touch and the 
most delicate change in the pressure of the air or the water 
that surrounds the organism." 
Now it is an accountable supposition that this pressure of 
water originally exercised a stimulating influence upon organ- 
isms prepared to secrete shelly coverings, and that while on the 
one hand the crustacean forms and inarticulate brachiopods in 
their evolution from annelidan ancestors along the shores, de- 
veloped their thin chitinous and phosphatic tissues, the mol- 
luscan and coelenterate life in the deeper waters was forcing 
its energies into the manifold elaboration of calcareous coats 
and skeletons. 
Dr. Dall in his address at the anniversary of the Biological 
Society of Washington on Deep Sea Mollusks indicated the 
conditions prevalent at the sea bottom. The great hydrostatic 
pressure, the presence of carbonic acid, sub-marine currents 
both acting as mechanical sweepers and food-carriers, darkness, 
the absence of vegetation, and a recourse for nourishment to 
k'oraminifera and the rain of pelagic organisms from the sur- 
face are therein mentioned. But perhaps as bearing on this 
question of the sudden evolution of the next fauna above the 
Cambrian, and which it is intended here to regard as of deep 
sea origin, are his reflections on the absence of conflict in the 
abyssal or archibenthal (semi-abyssal) regions. He said "the 
