105 
Presidential Address . By A. D. Michael. 
that it is not found in Spiders or Phalangiidae ? Or are we to go 
back to some common ancestor, which we suppose to have had the 
organ, which has lain dormant in all the numerous stages over vast 
periods of time, until Bdella was reached, and then suddenly reap- 
peared in full vigour? Or are we to suppose the Acarina to be 
derived from the Insecta ? If so, where is any trace of the organ in 
the intermediate stages, and why does it die out suddenly after Bdella 
without there being a trace of it in the most nearly allied creatures ? 
A very pretty little piece of apparatus which is peculiar to Bdella, 
although structures serving a similar purpose are known elsewhere, is 
the epipharynx. This is an organ which is somehow much neglected 
by anatomists, both in Insects and Arachnida, and yet it is of con- 
siderable interest, and of some importance. Oddly enough, it is 
frequently called the “ lingua,” although the two organs often co-exist 
in the same creature, and although a true lingua arises from the 
door of the mouth below the pharynx, while the epipharynx, as its 
name implies, is above the opening of the pharynx, and in the Acarina 
usually springs from the anterior upper edge of the pharyngeal tube, 
and projects freely into the mouth-cavity, forming a kind of pent-house 
overhanging the entrance to the alimentary canal, and probably 
guiding the food into the opening. It is usually a stiff, more or less 
elongated, lanceolate or triangular blade ; the latter is the shape in 
Bdella, but from its sides in that creature a broad membranous border 
hangs down like a curtain at the side of the food-stream. It must 
be remembered that Bdella is a predatory creature living by suction, 
and is a member of that group of Acari where no certain connection 
has been found between the ventriculus and the hindgut. It does not 
appear to pass solid dejecta, and therefore it is important that none 
should enter the canal. This is effected in the Acari of this genus 
which I have dissected by the epipharynx in the following manner. 
The lancet-shaped piece with its membranous edge is not the whole 
of the apparatus ; some little way below it is a thin horizontal semi- 
lunar membrane with its convex edge forward ; its upper surface and 
its curved edge bear regular series of teeth like those of a saw. The 
membrane is very transparent, and quite flexible, so that in its 
ordinary position it falls downward, making the upper surface the 
anterior, and of course, presenting the teeth towards the mouth. The 
largest teeth are at the edge ; they fall in front of the opening of the 
pharynx, and their points fall between a set of minute wart-like ele- 
vations on the floor of the mouth ; thus a grating is formed which 
effectually strains all solid particles out of the fluids which are sucked 
into the pharynx. 
The brain in Bdella has a peculiar interest for the following 
reason. When last year I showed you a picture of the almost 
globular brain of one of the Hydrachnidee, w 7 ith the nerves springing 
from it, and the small round hole in the centre affording a passage 
for the oesophagus right through it ; and when I told you at 
