ORGANIC DEPENDENCE AND DISEASE 
55 
tions, the interpretation may seem invasive. Nothing, I am 
disposed to believe, can be more illuminative of the prog- 
ress toward and in intelligence than the early case before 
us, in which a directed habit has already become fixed by 
heredity. 
Taken as a whole this combination is very complicated 
commensalism from a date so ancient as the Devonian, more 
extreme than any other yet known from the Paleozoic rocks. 
We find a somewhat parallel case in the present fauna de- 
scribed by Bouvier as occurring in the Gulf of Aden — a 
coral and a worm growing together, and hidden in the coral 
substance a gastropod on which both settled down when the 
partnership began ; furthermore there appears to be a small 
bivalve in association with the worm. Other similar cases 
might be cited from the existing fauna. 
One stands with wonder before such evidence as this from 
the ancient faunas, questioning how such a habitude came 
about, what conditions impelled, stabilized and restricted 
it, and our wonder is none the less because here we stand 
at the inception of such associations and contemplate it 
from a world that is full of them today. And the inquiry 
naturally arises : What became of this organic combina- 
tion? It reached its acme only as the coral genus became 
old, indeed in the last of its representatives. Piddled with 
commensals, overloaded with boarders who fed at the same 
table and flourished, it may be that the worm became an 
effective parasite which helped to bring about the extinc- 
tion of its host. 
Commensalism between the worms and sponges. This 
combination appears in the late Devonian, but there is evi- 
dence that it is of earlier date. We have just cited the 
presence of a minute sponge in the Hicetes innexus, the in- 
colant worm of Pleurodictynm, and there is an undescribed 
spreading sponge of the Middle Devonian (Hamilton 
group) which indicates the presence of coexistent annelids. 
The simple ancient instance I can here illustrate is that 
