Picture - Cosmic Polymath

(86 DESIGN IN NATURE
PLATE LXXXIX
PLATE LXXXIX (continued)
At F there is thickening of the achromatic fibres in middle of spindle indicating plane of
I. Repetition of dividing process with formation of spindles in daughter nuclei.
J. Results of division (Strasburger).
§ 75. Reproduction in the Bird.
division of cell.
The reproductive process can be readily and conveniently studied in the barn-door
fowl. The egg, which represents the female element of the bird, must in every
instance be impregnated or quickened by the presence, contact, or actual admixture
of the male element. This impregnation, as a rule, occurs at an early stage, when the
eggs are being formed. The formation and descent of the quickened egg down the
oviduct are among the most interesting and beautiful processes in nature, and afford
unmistakable evidences of design (Fig. 76).
Fig. 76.—Shows ovary, oviduct, and eggs of common barn-door fowl, a, Ovary, with eggs at
various stages of development ; h, Graafian follicle from which an egg has been discharged ;
c, fimbriated extremity of oviduct with egg entering it ; c, d, d\ portion of oviduct supplying
egg with moisture and twisted chalaziferous membrane (e,/) ; d, g, h, portion of oviduct engaged
in providing the egg with a coating of albumen (the white of the egg) ; h, i, j, portion of the
oviduct furnishing the three membranes of the egg (two soft and one hard) (after Dalton).
The young egg is formed in the ovary (Fig. 76, a, 6) and consists of a germinal vesicle,
a yolk, and a vitelline membrane. At this stage the egg is far from complete. It is
dropped into the fimbriated extremity (c) of the oviduct, the mucous lining of which
provides it with various coverings and membranes, soft and hard. Thus the upper
part of the oviduct (c, d) supplies it with fluid to make it more flexible and yield-
ing ; a second part {d, d') with a gelatinous membranous deposit which forms the
chalaziferous membrane (e, /) twisted at either end as if to prevent the escape of the
provides it with layers of a gelatinous albuminoid
vitellus ; a third part {d', g)
substance known as the white of the egg ; a fourth part (gr, h) furnishes it with three
membranous layers (the external, middle, and internal fibrous membranes) ; a fifth
part {i, j) infiltrates the external membrane with lime to produce the hard shell, the
internal and middle membranes forming the soft shell. The egg of the fowl, it will be
seen, is added to and completed in its passage down the oviduct. The completed egg
is shown at Fig. 77. Nor does the marvel stop here. The egg while it is being formed
is steadily passed along the oviduct by a series of peristaltic, rhythmic movements akin
to what occur in swallowing and in the passage of food along the intestine. At one
portion of the oviduct the egg is made to rotate, with the result that the chalazi-
ferous membrane is twisted in opposite directions to form the chalazse. The oviduct
at once completes and transmits the egg prior to its discharge through the cloaca.
This it does by providing various secretions and membranes, and by establishing a
series of spontaneous, independent, vital movements. The egg does not at any stage of its progress along the
oviduct
act as an irritant or stimulus either for the production of the secretions or the peristaltic movements.