220 



GENERAL OENITHOLOGY. 



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

 albumen, and finally a chaft 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 

 mammal result from tlic union of both miillerian ducts ; 

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

 developed. Functionally, tlie oviduct is also analogous (p. 

 68) til the mammalian uterus, inasmuch as it transmits the 

 product of conception, and detains it for a wliile, in the initial 

 stage of its germination, as we shall see in the sequel ; thtjugh 

 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. Tliese structures — ovary and o\'iduct, 

 tig. 108, — are most conveniently described as we trace tl»' 

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

 record diii'ers considerably fi'om the corres]ionding 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 iu the body of the parent, does not 

 require. The process is teruied ovulation. Ovulation, which 

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

 mestic fowl, in activity; from Owen, ,yit]i gcrmmation, which is the formation of a bird in the egg. 



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



rian ova, in all stages of develor- ■^"'^ former can be accomplished l)y tlie virgm bird, which 



meiit ; 7), a rii.e one ; c, its stigma, may lay eggs scarcely differing in appearance from those which 



Llyx ruptures: , , ~ ' ^ . 



liavo been iceundatcd, but genmuation in which is of course 



wliere the ovisac or calyx rujit 



(1, a ruptured empty calyx, to be al'- 



Borbed; «, infundibulum, or funnel- impossible. The course of ovulation, and afterward of gcrmi- 



sbaped orifice of tlie oviduct; /", next i- ■ i i '" 



portion of oviduct; ;i, follicnlar part "ation, is now to be traced. 



of oviduct; 7)?, mesometry, membrane 



steadying tlie oviduct ; the reference- ^. i *- mi, i ■ . ... 



line, m, crosses the constricted part or Ovulation. — 1 he ovum begms as a microscopic point m 



isthmus of the oviduct; these parts the ovary, the stroma or tissue of which is pticked with these 



secrete the white of the egg: /.'.shell- .... ta ■ • -j-- i • ^ i.i i r ■> 



forming or uterine part of oviduct, mf-Tient eggs. It IS primitively just like any other female 



in whicli is a completed egg, i ; I, Di/naiiiamo;ha, from that of a sponge up to tliat of a woman, 



lowest or vaginal part of oviduct. i j - i„ „n . i i r i -i ■^. ,. i . i 



opening into uro-gcnital sinus of the - '^ '"''^^'''^ ^"""P^'' '''■^^' ^"'1"^'^^': "* exhibiting active amoeboid 

 cloaca, 71,- o, anus. movements. It consists of a finely granular protoplasm, the 



vitellus, or yeU, enclosed in a delicate structureless cell-wall, the viteUine membrane, called 

 the zona peUucida from its appearance under the microscope. Imbedded in the vitellus is ;i 

 nucleus, or kernel, the (lerminal vesicle; in this is a uuclecdus, or inner kernel, the germimjl 

 spot. The ovum occupies a tiny space in the ovary, the cellular walls of which constitute ;ui 

 ovisac, or graafian follicle. Now if such an ovum as this \vere iii;imm;ilian, if would, without 

 material change, burst the ovisac, be received into the fallopian tube and conveyed to the 

 uterus; wliere, supposing it already fertilized, the whole of its contents would develoji info the 

 body of the emliryo. It would therefore be holohlastic (Gr. oXor, holos, the whole; ffKarmKos, 

 blastiJcos, 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 nourishinent of the 

 developing chick, thus separated from the tissues of its mother. Such provision is made by 

 the accumulation about the ovum of a gi'eat quantity of granular protoplasmic substance, whicli 

 forms nearly nil the large yelhiw 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 during 



