NATURAL HISTORY STUDIES 



simple means. Take, for instance, the " snow 

 shoes " of the North American Ruffed Grouse 

 (Bonasa umbellata). According to Dr. Austin 

 Hobart Clark, these "snow shoes " develop in 

 winter as two rows of firm plates on each side of each 

 toe, and they increase the area of the foot by as much 

 again. They remind one a little of the scolloped 

 margins of the toes in a grebe. Their effect is that 

 the bird is able to tread on the lightly-compacted 

 snow without sinking in. 



The Chick's Egg -Tooth 



An adaptation that makes one think is the " egg- 

 tooth " found at the tip of the bill in many young 

 birds, and used to help to break a way through 

 the imprisoning egg-shell. It is a hard thickening 

 of horn and lime at the tip of the bill, and since it 

 develops before the horny ensheathment of the beak, 

 it may be a residue of a very ancient scaly armature 

 in reptilian ancestors of birds. Be this as it may, 

 the instrument is an effective one, and it is used only 

 once ! What happens is this : the young bird ready 

 to be hatched changes the sideways position of its 

 head by means of certain muscles, the trigger being 

 pulled by a rather intricate change in the constitu- 

 tion. A few days after the chick is hatched the 

 egg-tooth falls off. It has served its purpose. 



The Mermaid's Purse 



Every one who lives on the coast is familiar with 

 the egg-cases of skate and dogfish, the so-called 

 mermaid's purses. These are quadrangular sacs 



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