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Transactions of the Society. 
the same time that that nearly spherical mass had been derived 
from distinct supra- and subcesophageal ganglia, you might well 
he excused if you felt somewhat incredulous. My mouth was 
then closed as to the anatomy of Bdella, a creature of a closely 
allied sub-family ; now I am able to show you a drawing of it 
carefully made from actual dissections. You will see here 
that the large sub-oesophageal ganglion is a flattened, almost 
oblong, sheet of nervous matter, with the actual nerves penetrating 
far into it in plainly discernible courses ; while the small, almost 
cubical, supra-oesophageal ganglion is perched on the anterior end of 
the lower ganglion, and is sharply demarcated from it. Both are 
slightly excavated for the passage of the oesophagus between the 
two. 
We should be inclined to say from this that Bdella was a primi- 
tive form amongst Acari, and one of the nearest to other groups such 
as the Insecta, from a phylogenetic point of view, but the result of 
further inquiries into the anatomy of the creature shows how difficult 
such tracings of phylogeny really are, and how complicated are the 
questions that arise during the inquiry ; and we may also learn how 
easy it is to draw up phylogenetic trees if we confine our attention to 
the particular organs which we are thinking of at the time, and how 
delusive those trees may be when so drawn up ; for in spite of the 
somewhat primitive character of the brain in Bdella, as compared 
with that in most other Acari, some other systems of organs in this 
animal are far more specialised and complicated than the correspond- 
ing parts in any other known Acarine ; I think I might say, than 
those in any other known Arachnid. These highly specialised 
portions of the anatomy are the male genital organs and the salivary 
glands. The great size, variety, and peculiarity of the latter are very 
remarkable, while the complication of the former, and the variety, 
size, and unexpected and special characters of the numerous accessory 
glands and other organs included in them are really quite startling. 
I wish I had time to describe to you even a few of the many inter- 
esting features of those organs, but it would be hopeless to attempt 
to do so to-night ; anyone interested in them will find them described 
in the Transactions of the Linnean Society. 
And now I have only to thank you once more for the unfailing 
courtesy and kindness which I have received at your hands during 
my long occupation of this chair, and to bid you farewell as your 
President, although I hope to remain for many years one of those 
connected with your Society in a humbler capacity. 
