12 EGGS AND EGG-COLLECTING. 
degree than the Duck can bestow on her progeny, which 
take four weeks to hatch. 
To still further illustrate this wonderful regulating 
principle, let us diverge for a moment from the eggs of 
birds to those of fish, where we find things adapted with 
incredible precision to the surrounding conditions of exist- 
ence. I have noticed that trout living and being obliged 
to deposit their ova ina stream subject to great variations 
of temperature, spawn much earlier than trout in a stream 
preserving a comparatively even temperature. The con- 
dition of the latter in comparison with the former showed 
unmistakably that the difference of food supply did not 
account for it, and as the fry in both streams appeared 
about the same time in the spring, and exhibited no 
appreciable difference in size or strength during the 
summer, the natural conclusion to be arrived at is that 
the time required for hatching in each stream is contem- 
plated and provided against in some mysterious way. 
Mechanical Construction of Eggs.—We now come 
to another phase of the protective principle, even more re- 
markable than those we have already discussed, and equally 
useful. This is in the mechanical construction of eggs to 
suit their situation and surrounding conditions. What an 
admirable provision Nature has shown in placing the axis of 
a bird’s egg just where it will prevent it rolling off a flat sur- 
face, such as a ledge of rock, when moved by the terrible gusts 
of wind that sweep over high latitudes, or perhaps roughly 
moved by the parent-bird suddenly fluttering off when scared. 
Take, for example, the egg of the Guillemot. This is 
so wonderfully constructed that if moved it will not roll 
away like a marble or billiard-ball, but simply spins round 
on its axis, in the same way as a screw or top, showing 
