330 Ridley.— On the method of fertilization in 
insect generally begins at the tips of the sepals, by the time 
it has got into the position for fertilizing the flower it has 
licked the sepals quite clean ; so it flies off to another one, 
where the same operation is repeated, and the pollen placed 
upon the stigma of the second flower. The fly with the pollen 
upon its back is less active than when free, the pollen ap- 
parently being an appreciable weight to it ; and it seems to me 
probable that, owing to this extra weight, the fly may on a 
second visit fall off the lip more rapidly, and so, falling a little 
lower, strike the stigma with the part of its abdomen with 
which it struck the pollinia before : but this I have not been 
able definitely to prove, and indeed there is the less need for 
it, because it must be remembered that when the fly strikes 
the viscid disc of the pollinia, the latter are at right-angles 
to its body; but when they are extracted, they fall by their 
own weight and lie at full length upon the insect’s abdomen, 
which they partially cover. 
It is essential that the fly’s whole weight should be thrown 
upon the lip ; one or two of its legs will not do, and smaller 
insects, as an ant or a thrips, will not pull over the lip. And a 
considerable amount too of pressure upon the pollen is re- 
quired. A fly wandering about the sepals often puts its wings 
into the stigma, or on the pollen-mass, but does not move it. 
In one form of the plant which I have seen, from Borneo, 
the flower is much smaller, and shorter. In this case the 
arrangement is less successful, because some of the flies can 
reach quite across the broadest part of the sepals and hold 
on by the edges, so that they do not slip at all. It is there- 
fore a decided advantage to the plant to have the flowers of 
large size, but the small-flowered form has one advantage, and 
that is a saving of time ; for there being so much less area of 
food-supply it takes a much shorter time for a fly to work over 
the sepals in this form than in the other. I watched one fly 
for over an hour before it got into a position for fertilizing the 
flower, and long before this occurred, a fly appeared from a neigh- 
bouring plant with smaller flowers with a pair of pollinia upon 
its back. I should state, however, that three or four flies 
