The President's Address. By A. D. Michael. 31 
startling to find Acari there. But if there he one creature more than 
another which we suppose to be always on the watch to devour its 
neighbours, and which we should think that Mites and small insects 
would avoid if they could, it is probably a spider ; there is one called 
Amaurobius ferox , whose character does not belie its name ; it lives in 
a silken tube, which it spins for itself under large stones, with floccu- 
lent threads round the mouth of the tube, which serve to catch its 
prey. I wanted some Bdellse (a sub-family of Trombidiidse), but it 
was late in the season, and I could not find many. I, however, found 
a few scattered specimens under stones on the walls of the fields. 
One day to my surprise I saw two or three on a web of Amaurobius 
ferox, and thought they had been caught, but I shortly afterwards 
found another web with some more on. When I looked at them they 
certainly were not caught, but ran about quite at their ease. Finally 
I found that this was so common that when I wanted the Bdellse the 
best way of collecting them was to hunt for the webs of the spider. 
On these webs I found them of all ages and both sexes, often a great 
many on a single web. There w^ere active ones and inert ones under- 
going ecdysis, but, as far as I could see, the spider never touched any 
of them. If near the web when disturbed, they usually retreated to 
its shelter ; they ran about it quite easily, and seemed to me to regard 
it as a home. It is easy to see what benefit the Bdella gets 
from the association, provided it is not eaten ; it finds a home on the 
web, it probably is protected from its own enemies by the terror of 
the spider, and Bdella is generally supposed to be predatory, and 
though I cannot vouch for this, I should think that it is probably 
correct ; if so, it doubtless gets the benefit of very small flies caught 
in the web, which are beneath the notice of the spider. But what 
benefit the spider receives from the Bdella is, I confess, at present 
entirely beyond my comprehension. The Bdellse were all of one 
species, which was found elsewhere, but far less commonly. 
One other matter which arose in my late investigations into the 
reproductive organs of the Gamasinae I will mention, because you 
probably have not seen it in the Transactions of the Linnean Society, 
and it may interest you, although the whole investigation would be^v 
far too lengthy to give even a sketch of to-night. This point is the 
mode of coition. The male genital opening of most of the Gamasinae 
is immediately behind the rostrum, and is simply a hole, not provided 
with any erectile or extensible intromittent organ. The form of the 
parts would not allow of this aperture being applied to the female ; 
how, then, was fertilization effected ? On that point there was not 
any reliable information. Gamasidae mostly have very long, ex- 
tremely extensible, chelate mandibles. Although those of the females 
show but little difference, yet in a large number of species the male 
mandible is entirely different, not only from the female mandible 
of its own species, but from the males of other species. The varia- 
tions are most strange and curious, the mandible being provided 
with great projecting pieces of bizarre and complicated forms, some 
