. Key to North American birds. Containing a concise account of every species of living and fossil bird at present known from the continent north of the Mexican and United States boundary, inclusive of Greenland and Lower California, with which are incorporated General ornithology: an outline of the structure and classification of birds; and Field ornithology, a manual of collecting, preparing, and preserving birds. Birds; Birds. 220 GENERAL OBNITHOLOGT. duct) which conveys the ripened ovnm, and in its passage provides it with a quantity of white alhumen, and finally a chalk shell. A bird's ovi
. Key to North American birds. Containing a concise account of every species of living and fossil bird at present known from the continent north of the Mexican and United States boundary, inclusive of Greenland and Lower California, with which are incorporated General ornithology: an outline of the structure and classification of birds; and Field ornithology, a manual of collecting, preparing, and preserving birds. Birds; Birds. 220 GENERAL OBNITHOLOGT. duct) which conveys the ripened ovnm, and in its passage provides it with a quantity of white alhumen, and finally a chalk shell. A bird's oviduct is the strict moi-phological homologne (p. 68) of a mammal's fallopian tube, uterus and vagiua,— more accurately, of one fallopian tube, one half of a utems, and one half of a vagina; for the uterus and vagina of a mammal result from the union of both muUerian ducts; whereas ia a bird only one — the left usually — is normally developed. Functionally, the oviduct is also analogous (p. 68) to the mammalian uterus, inasmuch as it transmits the product of conception, and detains it for a while, in the. initial stage of its germination, as we shall see in the sequel; though all but the very first steps in the development of the chick are taken during incubation, the egg having so hastily left its uterine matrix. These structures — ovaty and oviduct, fig. 108, — are most conveniently described as we trace the course of the ovum from its origination to its maturity. This record differs considerably from the corresponding course of events in a mammal, inasmuch as the ovum of a bird, though primitively identical with that of any other animal, acquires special albuminous and cretaceous envelopes which the mam- malian ovum, developed in the body of the parent, does not require. The process is termed ovulation. Ovulation, which Fig. 108. — Female organs of do- is the fonnation of an egg in the bird, must not be confounded mesdc fowl, in activity; from Owen, with germ inati
Size: 1131px × 2210px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectbirds, bookyear1894
