CHAPTER X 



birds' eggs 



§ I. The Making of the Egg. § 2. Yolk-forming. § 3. Maturation 

 of the Ovum. § 4. The Male Reproductive System. § 5. Fertili- 

 sation. § 6. The Further History of the Fertilised Ovum. 

 § 7. Early Development. § 8. Hatching. § 9. The Natural 

 History of Birds' Eggs.* § 10. Possible Uses of Egg- Coloration. 

 § II. Fertility and Fecundit>^ § 12. Sterility. 



Many reptiles lay eggs essentially like those of birds^; those 

 of tortoises and crocodiles are not very different from those 

 of pigeons and geese respectively. Some reptiles have eggs 

 whose shells are still flexible, and this represents a stage in 

 the development of the bird's egg. It may be said that, as 

 regards eggs, birds have given finishing touches to what 

 reptiles elaborated. 



§ I. The Making of the Egg 



The history of the individual egg begins in the ovary, 

 which has the appearance of a bunch of grapes and is attached 

 to the wall of the body-cavity on the left side. There are 

 to begin with two ovaries, but, for some unknown reason, 

 the right ovary disappears and its oviduct dwindles to a 

 vestige. As the breeding season sets in, the immature ova 

 on the surface of the ovary begin to accumulate yolk, and 

 many different sizes can be seen. When the egg is ripe it 

 bursts from its encapsuling follicle and is caught up by the 

 trumpet-shaped mouth of the oviduct. But it is necessary 

 to look into these matters more closely. 



Origin of the Gonads, — Where, it may be asked, do the 

 reproductive organs or gonads come from ? The answer in 

 the chick seems quite clear that they arise from primitive 



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