326 GENERAL ORNITHOLOGY part ii 



both Miillerian ducts ; whereas in a bird only one— the left usually 

 — is normally developed. Functionally, the oviduct is also analo- 

 gous (p. 103) 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 — ovary and oviduct. Fig. 108 — are most con- 

 veniently 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 mammalian ovum, developed in the body of the parent, does 

 not require. The process is termed ovulation. Ovulation, which is 

 the formation of an egg in the bird, must not be confounded Avith 

 germination, which is the formation of a l^ird in the egg. The 

 former can be accomplished by the virgin bird, Avhich may lay eggs 

 scarcely differing in appearance from those which have been fecun- 

 dated, but germination in which is of course impossible. The course 

 of ovulation, and afterward of germination, is now to be traced. 



Ovulation. — The ovum begins as a microscopic point in the 

 ovary, the stroma or tissue of which is packed with these incipient 

 eggs. It is primitively just like any other female DynamamKha, 

 from that of a sponge up to that of a woman — a naked simple cell, 

 capable of exhibiting active amoeboid movements. It consists of a 

 finely granular protoplasm, the vitellus, or yelk, enclosed in a delicate 

 structureless cell- wall, the vitelline memhrane, called the ^ona j^eUucida 

 from its appearance under the microscope. Imbedded in the vitellus 

 is a nucleus, or kernel, the germinal vesicle ; in this is a nucleolus, or 

 inner kernel, the germinal sjjot. The ovum occupies a tiny space in 

 the ovary, the cellular walls of which constitute an ovisac, or Graafian 

 follicle. Now if such an ovum as this were mammalian, it would, 

 without material change, burst the ovisac, be received into the Fallo- 

 pian tube and conveyed to the uterus ; where, supposing it already 

 fertilised, the whole of its contents would develop into the body of 

 the embryo. It would therefore be holohlastic (Gr. oAos% holos, the 

 whole ; fSXaa-riKos, hlastikos, germinative). It is different with a 

 bird or other " oviparous " animal, the egg of which has to hatch 

 outside the body ; for provision must be made for the nourishment 

 of the developing chick, thus separated from the tissues of its 

 mother. Such provision is made by the accumulation about the 

 ovum of a great quantity of granular protoplasmic substance, which 

 forms nearly all the large yellow ball called in ordinary language 

 " the yelk " of an egg. None of this adventitious substance goes to 



