116 HABITS OF BIRDS. 



generally built on trees, and whose progeny are born 

 blind and forlorn. Thus the folliculi in the eggs 

 fowls, partridges, and moor-hens, are of considerable 

 extent, whilst those in the eggs of crows, sparrows, 

 and doves are extremely contracted; the chicks, 

 therefore, of fowls and partridges have a more per- 

 fect plumage, and a greater aptitude to locomotion, 

 than the callow nestlings of doves and sparrows. 

 Such an instance of the agency of oxygenation in 

 the promotion and increase of muscular power is not 

 solitary in physiology ; for the history of ruminating 

 animals will furnish us with a parallel example." 

 " Their cotyledons," observes the author of ' Zoono- 

 mia/ " seem to be designed for the purpose of ex- 

 panding a greater surface for the termination of the 

 placental vessels, in order to receive oxygenation 

 from the uterine ones : thus the progeny of the 

 class of animals are more completely formed before 

 their nativity, than that of the carnivorous classes. 

 Calves, therefore, and lambs, can walk in a few 

 minutes after their birth ; while kittens and puppies 

 remain many days without opening their eyes." 



" It is," continues Dr. Paris, " a very curious fact 

 well known to every one employed in the concerns of 

 the farm-yard, that if the obtuse extremity of an egg 

 be perforated with the point of the smallest needle (a 

 stratagem which malice not unfrequently suggests) 

 its generating process is arrested, and it perishes like 

 the subventaneus egg. Hence Sir Busick Harwood 

 was led to suspect that the elastic fluid contained in 

 the air-bag was oxygen, and I was induced to ex- 

 amine its nature. Can this curious problem be 

 solved by supposing that the constant ingress of fresh 

 air is too highly exciting ? A parallel example may 

 be adduced from the vegetable kingdom in support 

 of such an opinion. The young and tender plant, 

 before it puts forth its roots, is often destroyed by 



