PROCEEDINGS OF SECTION D. 235 
&c.). This, then, is a case of differing natural conditions pro- 
ducing variation of form. 
The close adhesion of the aerial roots to the parent pseudo- 
bulbs brought to my mind a problem which puzzled me a good 
deal at one time, namely, the method by which aerial roots of 
epiphytal orchids adhere so closely to the trunks of trees, rocks, 
or, in cultivation, to flower pots. In removing them from their 
support it will often be found that the roots split, and leave a 
part adhering tightly to the tree or rock on which they live. 
Since I began growing them, however, I have repeatedly 
noticed that if the green-growing point of the root be soaked 
either by rain or in watering them, a transparent mucilage 
exudes, and this coming in contact with anything sticks firmly 
and holds it to the support when dry. I have noticed this par- 
ticularly in Clezsostoma tridentatum and Dendrobium emulum. 
EXPLANATION OF PLATES. 
Vv. 
Fig.1 Dendrobium enulum ... ays ... Southern form. 
Fig. 2 BA 5 a2) er ... Form under cultivation. 
Fig. 3 re re ae as ... Northern form. 
VI. 
Fig.4 Dendrobium tetragonum Es .... Ordinary form. 
Fig. 5 Mf Ss 4 ... Proliferous form. 
10.—NOTES ON A COLLECTION OF BIRDS FROM 
WESTERN AUSTRALIA. 
By! RCH acy: 
11—NOTE ON THE FAUNA OF THE GILL-CAVITIES OF 
FRESH-WATER CRAYFISHES. 
By Wi.tiiam A. Haswett, M.A., D.Sc, F.R.S. 
An examination of the contents of the branchial chambers of 
Australasian fresh-water crayfishes has revealed an extensive and 
varied assemblage of animals that pass their entire lives in this 
sheltered position, and are never to be met with elsewhere. In 
addition, there are some that, though so far they have only been 
found in this situation, are in all probability not restricted to it, 
and are to be looked upon rather as chance visitors than constant 
members of the population. Some of these inhabitants of the 
branchial chambers are not, in any sense, parasites: others, ap- 
