THE POLLINATION OF SATYRIUM BICALLOSUM, THUNB. 151 
bodies for insects, as I found the cells of which they are composed to be full 
of fine raphides of calcium oxalate (Figs. 1, 2 and 3). 
From the above description, it will be realised that each half of the flower 
has its own entrance, with its alighting place for insects; its own pollinium, 
with adhesive disc projecting laterally into the passage, and its own stigmatic 
surface, placed just above the adhesive disc. Each half of the flower also has 
its own spur. The possibility of the separate functioning of the halves of a 
zygomorphic flower is of great interest. In the case of actinomorphic flowers, 
we have Iris, with three “entrances,” but instances of zygomorphic flowers 
with separately functioning halves are very rare. It will be of value, for 
purposes of comparison, to determine the pollination mechanism in S. Lindley- 
anum, Bolus, in which species the flower is not so completely divided into 
distinct halves, and in which the viscid discs are directed towards the front 
of the flower. 
After the above structural details had been observed, it became necessary 
to seek for the pollinating insects. As there was a possibility of insect visits 
at night, and the plants were growing upon a steep mountain side, several 
miles from a house, it seemed likely that a prolonged watch would have to be 
kept. 
I was fortunate enough to discover the insect in a fashion which conveys a 
useful suggestion to those interested in orchid pollination, and which is there- 
fore worth recording here. The plants were growing in a moist place where there 
was a trickle of water through the soil, from the mountains behind. I noticed 
numerous plants of Drosera hilaris, Ch. and Schl. in the same locality, and 
it occurred to me that if I could find a Satyrium plant in the centre of a 
group of Drosera, I might find the pollinating insect already captured. I soon 
discovered the required combination; a fine Satyrium, almost entirely sur- 
rounded by Drosera. On examining the leaves of the latter, no less than a 
dozen small black flies were seen to have become stuck to the tentacles, each 
fly with one, two, or even three pollinia attached to it. 
I am indebted to Mr T. R. Edwards, of the British Museum, foi the 
identification of this insect. He informs me that it is a species of Sciaia , of 
the Family Sciarideae. The larvae live in rotting wood and decaying 
vegetable matter. 
After a further search in the vicinity of the Satyrium flowers, 1 discovere 
two other specimens of the fly, one bearing two pollinia on the left side of tin 
thorax at the base of the wing, and one bearing three pollinia in flit com 
sponding position. 
The insects were running rapidly over the ground, and did not take 1 
even when disturbed. No doubt they were overburdened by the po mia, 
which are large in comparison with the insects bearing them. These 0 sen a 
tions were made at 12.30 p.m., October 2nd, 1920, the weather at that 
