CHAPTER II 

 THE GAMETES AND FERTILIZATION 



THE OVARIAN OVUM; MATURATION, OVULATION, AND FERTILIZA- 

 TION; THE FORMATION OF THE ACCESSORY COVERINGS OF 

 THE OVUM; THE STRUCTURE OF THE EGG AT THE TIME OF 



LAYING; INCUBATION. 



The Ovarian Ovum. The formation of the ovum, the phe- 

 nomena of fertilization, and the stages of development occurring 

 prior to the laying of the egg have been more completely worked 

 out in the pigeon than in the hen. The observations which 

 have been carried out on the hen's egg indicate, as might be 

 expected from the near relationship of the pigeon and the hen, 

 that the processes in the two forms are closely comparable. 

 The following account which is based chiefly on observations 

 made on the pigeon's egg may, therefore, be taken to apply 

 equally well in all essentials to the hen's egg. 



The part of the egg commonly known as the "yolk" is a 

 single cell, the female sex cell or ovum. Its great size as com- 

 pared with other cells is due to the food material it contains. 

 While the egg cell is still in the ovary, material which is later 

 used by the embryo as food is deposited in its cytoplasm. This 

 deposit which is known as deutoplasni consists of a viscid fluid 

 in which are suspended granules and globules of Various sizes. 

 As the deutoplasm increases in amount the nucleus and the cyto- 

 plasm are forced toward the surface so that eventually the 

 deutoplasm comes to occupy nearly the entire cell. This 

 abundance of deutoplasm accumulated in the ovum furnishes 

 a readily assimilable food supply, which makes possible the 

 extremely rapid development of the chick embryo. 



A section of the hen's ovary passing through a nearly mature 

 ovum (Fig. i) shows the ovum and the tissues which surround 

 it projecting from the ovary but connected to it by a constricted 

 stalk of ovarian tissue. The protuberance containing the ovum 

 is known as a follicle. The bulk of the ovum itself is made up of 



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