15 



birds above adverted to, varies almost always in correlation with 

 the size of the bird. 



Thus among the Hesthogens we find the Partridge sits 21 days; 

 the Pheasant, 24 to 26 days ; the Guinea Fowl, 28 or 29 days ; 

 the Turkey, 30 days ; the Swan, 40 to 45 days ; the Emeu, about 

 60 days. 



Among the Gymnogenous Birds the smallest species are found, 

 and the period of incubation varies with their size. The Hum- 

 ming Bird sits 12 days ; the Whitethroat, 13 days ; Canaries, 13 to 

 14 days; Starlings, 16 days; Pigeons, 16 to 17 days; the Eaven, 

 20 days ; the larger Eagles and Vultures, several weeks, but the 

 exact duration of their incubation is not well known ; they build 

 in inaccessible place, and but few observations have been made. 



With regard to the length of time occupied in arriving at the 

 full size, by birds after their escape from the egg, there is a great 

 difference between those that are produced clothed and those 

 hatched naked. 



The latter, when young, have two parents always engaged in 

 feeding them, often with half digested food. The young ones 

 make almost no exertion to obtain food, and their growth to the 

 full size is consequently rapid ; but the time occupied varies with 

 the size of the birds. 



Wrens leave the nest in less than a fortnight after hatching ; 

 Linnets, Goldfinches, and other Finches remain but little longer 

 in the nest ; Thrushes and Blackbirds appear fledged and neaiiy 

 as large as adults in about a fortnight after being hatched. 



The young Raven is fully fledged when about one month old. 



The Eagles are from two to three months in the nest after being 

 hatched, and several species both of Eagle and Vulture do not 

 attain their complete adult plumage before the sixth year of their 

 age. 



Many of the smaller species of Gymnogenous birds have a suc- 

 cession of nests during the year. 



The familiar farmyard Hesthogenous birds conform to the rule 

 under consideration. 



The Turkey is longer in coming to maturity than the Fowl ; 

 the Goose than the Duck. 



Most birds acquire their full growth during the first year of 

 their lives, but the Ostriches, the largest of all birds, do not attain 

 adult size till they are two years of age. 



If my views are right as to birds, that the larger species occupy 



