THEIR REPRODUCTION (EGGS) 289 



connects the extreme type. These are Round, 

 Oval, and Pyriform. Round-shaped eggs are a 

 special feature in such groups as the Falcons, 

 Owls, Woodpeckers, Rollers, Kingfishers, Bee- 

 Eaters, and so forth. Oval eggs are specially 

 typical of the Sand-Grouse, Pigeons, Nightjars, 

 and Cormorants, but various modifications of 

 this form are common to the majority of birds, 

 from the biconical shape characteristic of the 

 Grebes to the more familiar form of those of 

 the Song Thrush and most Passerine species, as 

 well as in the Game Birds, Petrels, and many 

 others. Pyriform eggs are chiefly confined to 

 the Charadriiformes, such as the Plovers, Snipes, 

 and Sandpipers, but also occur in the Auks and 

 one or two other families. We are as yet unable 

 to say definitely why the eggs of birds assume 

 these various shapes, but certain hypotheses have 

 been put forward to account for them. One of 

 the most ingenious and attractive of these is that 

 of Dr. Nicolsky. This naturalist asserts that the 

 normal shape of an egg is spherical, and that 

 it becomes more or less elongated by pressure 

 from the walls of the ovary before the shell 

 is deposited. He makes the suggestion that 

 birds laying spherical eggs usually maintain an 

 upright position, in which the weight of the egg 



