220 



GENERAL ORNITHOLOGY. 



duct) which conveys the ripened ovum, and in its passage provides it with a quantity of white 

 albumen, and finally a chalk shell. A bird's oviduct is the strict morphological homologue 

 (p. 68) of a mammal's fallopian tube, uterus and vagina, — 

 more accurately, of one fallopian tube, one half of a uterus, 

 and one half of a vagina ; for the uterus and vagina of a 

 luammal result from the union of both uiiillerian ducts; 

 whereas in a bird only one — the left usually — is normally 

 develtjped. Functionally, the oviduct is also analogous (p. 

 68) 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 th(> sc(iuol ; though 

 all but the very first steps in the development of the chick 

 are taken during incubation, the egg haying so hastily left 

 its uterine matrix. These structures — ovary and oviduct, 

 fig. 108, — arfe most conveniently described as we trace the 

 course of the ovum from its origination to its maturity. This 

 record dififers considerably from the coiTesponding 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 mam- 

 malian ovum, developed in the body of the parent, does not 

 require. The process is termed ovulation. Ovulation, which 

 Fig. 108. - Female organs of do- is the formation of an egg in the bird, must not be confounded 

 mestic fowl, in activity ; from Owen, vpith germination, which is the formation of a bird in the esrg. 



after Cams, a, b, c, d, mass of ova- 



rian ova, in all stages of develop- 

 ment ; h, a ripe one; c, its stigma, 

 where the ovisac or calyx ruptures; 

 <J, a ruptured empty calyx, to be ab- 

 sorbed ; e, infundibulum, or funnel- 

 sliaped orifice of the oviduct ; /, next 

 portion of oviduct; g, follicular part 

 of oviduct ; m, mesometry, membrane 

 steadying the oviduct; tbe reference- 

 line, m, crosses the constricted part or 

 isthmus of the oviduct ; these parts 

 secrete the white of the egg ; k. shell- 

 forming or uterine part of oviduct, 

 in which is a completed egg, i ; I, 



The former can be accomplished by the virgin bird, which 

 may lay eggs scarcely differing in appearance from those which 

 have been fecundated, but germination in which is of course 

 impossible. The course of ovulation, and afterward of germi- 

 nation, is now to be traced. 



Ovulation. — The ovum begins as a microscopic point in 

 the ovary, the stroma or tissue oi which is packed with these 

 incipient eggs. It is primitively just like any other female 

 Dynamamoeba, from that of a sponge up to that of a woman, 

 lowest or vaginal part of oviduct, _'^ naked simple cell, capable of exhibiting active amoeboid 

 opening into uro-genital sinus of the -^ 7. f. i i ^ 



cloaca, ji. ; o, anus. movements. It consists of a finely granular protoplasm, the 



vitellus, or yell; enclosed in a delicate structureless cell-wall, the vitelline membrane, called 

 the zona pellucida 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 

 spot. The o^^^m 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 fallopian tube and conveyed to the 

 uterus ; where, supposing it already fertihzed, the wliole of its contents would develoi^ into the 

 body of the embryo. It would therefore be Jioloblastic (Gr. oKos, Jiolos, the wliole ; ^XaariKos, 

 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 f.f 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 form the embryo ; it is what the embryo feeds on duri!?£r 



