12 EGGS AND EGG-COLLSCTINQ. 



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 in a 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 



