(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). 



division of cell. 



§ 75. Reproduction in the Bird. 



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 

 vitellus ; a third part {d', g) provides it with layers of a gelatinous albuminoid 

 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 

 spontaneous, independent, vital movements. The egg does not at any stage of its progress along the 

 act as an irritant or stimulus either for the production of the secretions or the peristaltic movements. 



series of 

 oviduct 



