290 SIR JOHN LUBBOCK ON THYSANURA. 
against the ground with force enough to throw the Smynthurus so high up into the air. 
We see the difference very well in a crossbow; the muscular effort required to set the 
bow is much less than that which would be necessary to project the arrow as far if 
applied directly. One might suppose that though the force required to pull the spring 
forward might be much less than that necessary to move it backwards, still, as the 
spring is habitually carried with the points forward, there would be a constant strain 
in the one case, and only an occasional effort wanted in the other. 
When, however, the spring points straight forwards, there is perhaps little strain on 
it; moreover there is a little catch (Plate XLV. figs. 10 & 11), which is an organ homo- 
logous with the spring itself, but situated on one of the anterior segments; this passes 
between the twe arms of the spring, and keeps them in place. It answers in fact to 
the catch in a erossbow, and as soon as it is drawn forwards, the muscle pulls the spring 
downwards, and its own elasticity does the rest. 
A priori it might have been supposed that a position of rest was one of relaxation, in 
which the muscles were, so to say, at ease, but ready to spring up to attention in a 
moment if necessary. On the contrary, however, we find very often that a position of 
. rest is a state of opposite tensions. 
Take, for instance, our own case. The upright position which seems so easy and 
natural to man, is, says Prof. Huxley, in his excellent lessons in elementary physiology, 
* the result of the contraction of a multitude of muscles which oppose and balance one 
another. Thus, the foot affording the surface of support, the muscles of the calf must 
contract, or the legs and body would fall forward. But this action tends to bend the leg; 
and, to neutralize this and keep the leg straight, the great muscles in front of the thigh 
must come into play. But these, by the same action, tend to bend the body forward on 
the legs; and if the body is to be kept straight, they must be neutralized by the action 
of the muscles of the buttocks and of the back." 
I will take one more illustration from a very different part of the organized kingdom. 
In most of the Orchids, as Mr. Darwin has shown us in his excellent work on that 
order of plants, the pollen from one flower is carried by insects to another; and if this 
is not done, the flower is not fertilized and the seed is not developed. Now, in our own 
small Orchids, when an insect lights on the flower the sticky end of the pollinium 
adheres to the insect, and is thus carried away ; in some of the large tropical Orchids, 
however, the part of the flower which insects visit is so far from the pollen-masses that 
a different arrangement is necessary. In Catasetum, for instance, there is a long sensi- 
tive process, or antenna, which hangs over the part on which insects alight, in such a 
manner that they can scarcely fail to touch it. Directly they do so, the flower throws 
its pollen-masses in the direction of the insect, and with such force that they will fly 
two or three feet. I have myself seen a flower, when its antenna was touched, throw the 
pollen-masses for about two feet, across a small table and to a window,on which they stuck. 
This is not effected by muscular action ; but the stalk on which the pollen-masses stand 
is bent round a protuberance, and held in position by a delicate membrane. When the 
sensitive antenna is touched, this membrane gives way, and the sess of the pol 
stalk throws it forwards with much force, as just described. 
