PROCEEDINGS OF THE SOCIETY. 
391 
Mr. G. C. Karop could say little on the matter from personal 
experience, as lie did not possess and had had never been able to obtain 
a satisfactory amount of Podura scales to experiment with. Possibly 
a study of these and other scales from the developmental side might 
throw some light on the interpretation of their final structure, but, so 
far as he knew, there was no memoir on the subject. Arising, as they 
presumably did, as hollow vesicles which afterwards collapsed, the super- 
imposed membranes by infolding, puckering and contraction, might give 
rise to many of the usual appearances of these objects ; but the very 
considerable regularity of marking was hardly explicable on simple 
mechanical grounds alone, and quite obviously insufficient to account 
for separate featherlets as described by Mr. Letherby and other authors. 
Mr. J. W. Gifford said that the postage-stamp fracture appearance 
was borne out by his own photographs taken with monochromatic light 
by means of his screens ; the appearance always remained the same, and 
he therefore had no doubt as to its reality. 
The President did not know if he had correctly grasped the precise 
mode in which Mr. Letherby put the matter before them. In Insects, 
as a rule, every scale, no doubt, was distinctly formed of two mem- 
branes — it being, so to speak, constructed like a Japanese fan, of two 
strained surfaces over a skeleton between them. Did Mr. Letherby 
suggest that each of these was double, and that there were two perforated 
and two unperforated membranes, or did he intend to say that it was 
the upper or the under part which was perforated ? It would, of course, 
be very interesting to know that there were such perforations as those 
referred to. 
Mr. Letherby said he had seen many scales in which the two mem- 
branes were certainly separated, but he did not think there were more 
than two membranes, and it was the under one to which the stalk was 
attached. He had one scale on his slide where the upper membrane 
alone was attached to the cover-glass. He had no doubt about the 
perforations, but at present he could add nothing to what he had put 
before the meeting. 
The President thought it rather rash to prophesy as to what might 
be known in future, but there could be no doubt that the photograph 
exhibited was remarkably clear, and that their thanks were due to 
Mr. Letherby for this, and also for the very instructive note with which 
it had been accompanied. 
Dr. R. G. Hebb having been requested to occupy the chair, 
The President gave an interesting resume of his paper “ On the 
Form and Proportions of the Brain in the Oribatkke and in some other 
Acarina,” the subject being illustrated by drawings upon the black- 
board, and by some excellent sections exhibited under several Micro- 
scopes in the room. 
Mr. Nelson said the little he had done in connection with the subject 
consisted in making a few calculations based upon a number of drawings 
which Mr. Michael had sent to him. These consisted of figures of very 
irregular shapes, and the only thing to be done was to divide them up 
into more regular forms and then square out the contents. By way of 
testing the accuracy of this he made a model in accordance with the 
