148 THE INFANCY OF ANIMALS 



To appreciate the nature of the latter fact it is necessary 

 to remember that in most birds the skeleton of the beak 

 is formed by three bony beams — an upper forming the 

 ridge of the beak, and a right and left lateral forming its 

 sides. Enclosed within the space thus formed, and at 

 its hinder end, lie the cartilaginous walls of the olfactory 

 apparatus. Now, partly by the ossification of these walls, 

 and partly by the extension of bony matter by the thicken- 

 ing of the beams just described, the whole of the once 

 spacious chamber covered by the beak sheath is filled 

 up in all the birds mentioned in this connection save 

 the penguins. But in the Cape penguin, this process of 

 closing is far advanced, though even in very old birds 

 it is never carried so far as in, say, the cormorant or the 

 gannet. What the Cape penguin fails to do during its 

 whole lifetime, the gannet and the cormorant accomplish 

 before they leave the nest. In the embryo we find the 

 typical beak skeleton of three bony beams ; by hatching- 

 time the work of closing has begun, and by the time the 

 nest is left it is complete. 



One naturally seeks to explain these evidently related 

 facts. It is clear, from what obtains among the penguins, 

 that the aperture in the beak-sheath closed long before 

 any change began in the underlying bony structure. But 

 how the one reacts upon the other seems impossible of 

 explanation. More difficult yet to grasp is the reason 

 for the closing up at all. If only the cormorants and 

 penguins displayed these phenomena we should at once 

 be ready with an interpretation — the whole thing would 

 have been as clear as day ; for having regard to the fact 

 that the whole of the food of these birds must be obtained 

 by diving, we should therefore have explained the sup- 

 pression of the external nostrils as an adaptation to these 



