PRESIDENT’S ADDRESS. 321 
slight disturbanee, the animal can rapidly withdraw into 
safe quarters. It is outside the burrow that the process of 
procreation.takes place, the result of which is the formation 
(at a subsequent date) of a cocoon containing the eggs, 
which, in all the cases known to us, is deposited in the 
burrow. 
I am not taking into consideration the fresh-water worms 
(so closely allied to the earthworms), for the bionomical 
facts are different, as, indeed, are the distributional facts, of 
which but little is known. 
Let us consider for a moment the means by which earth- 
worms may be dispersed over the surface of the planet. 
The animals are killed by immersion im salt-water, as also 
are their eggs; so that, éven if they be carried away from 
their home embedded in the earth amongst the roots of a 
tree, or even in a rotten log, or any such object, they would 
soon perish, owing to the splashing of the sea, the rolling ot 
the tree, or the rapid disintegration of the earth at its roots. 
The chances of adhering to the feet or body of birds or 
mammals are extremely limited; for, if the worm were on 
the surface, the bird would devour it, rather than tread on 
it. Nor need we involve the agency of a mammal, for, in 
general, where a mammal can go, there also can an earth- 
worm travel. 
As to transference of cocoons on the feet of birds—in the 
way that small molluscs and some insects are believed to be 
_carried—the fact just mentioned, of the subterranean de- 
position ‘of the cocoon, renders this method improbable, 
except, perhaps, on very rare occasions, when some far-flying 
bird follows a plough, which may turn up cocoons. But 
this avails but little in discussing transference beyond the 
sea; for the cocoon would either dry up, and tho eggs die, 
or it might be washed off in the sea if it happened to have 
become attached to such a bird as a seagull. 
Dispersal by means of wind is equally out of the question, 
and that by icebergs or ice-sheet must be very rare. Still, 
we must bear in mind the possibility of the dispersal of 
small worms in this manner; for small Hnchytreids have 
been found embedded in ice on frozen ponds, and even in 
the glaciers of Alaska; but this will apply to but very few 
earthworms, since it is rare for them to live in water. 
In fact, any mode of assisted dispersal appears to be out 
of the question. There only remains the active migration 
of the earthworm in the earth. 
As you are aware, dispersal may be interfered with by 
barriers. What barriers exist in this case ? 
Ww 
