226 



GENERAL OBN UROLOGY. 



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

 albumen, and iinally 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 

 mammal result from the union of both miillerian ducts ; 

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

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

 68) to the mammahan uterus, inasmuch as it transmits the 

 product of conception, and detains it for a whUe, 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 conveniently 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 mamniiil, inasmuch as the ovum of a bird, though 

 primitively identical Avith 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 

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

 with germination, which is the formation of a bird in the egg. 

 The former can be accomplished by the virgin bird, which 

 may lay eggs scarcely differing in appearance irom 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. 



Fig. 108. — Female organs of do- 

 mestic fowl, in activity ; from Owen, 

 after Carus. 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 ; 

 rf, a ruptured empty calyx, to be ab- 

 sorbed ; e, infundibulum, or funnel- 

 sbaped orifice of the oviduct ; /, next 

 portion of oviduct ; g, follicular part 

 of oviduct ; in, mesometry, membrane 

 steadying the oviduct ; the reference- 

 line, m, crosses the constricted part or 

 isthmus of the oviduct ; these parts 

 secrete the white of the egg ; A-, shell- 

 forming or uterine part of oviduct, 

 in which is a completed egg, i ; I, 

 lowest or vaginal part of oviduct, 

 opening into uro-genital sinus of the 

 cloaca, n ; o, anus. 



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 

 Dynamamoeba, 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 

 viteUus, or yelk, enclosed in a delicate structureless cell- wall, the vitelline membrane, called 

 the zona 2)eHuci(la from its appearance imder the microscope. Imbedded in the vitellus is ii 

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

 spot. The ovum occupies a tiny space in the ovary, the ceUular 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 whole of its contents would develop into the 

 body f.f the embryo. ItVould therefore be holoblastic (Gr. o\os. holos, the whole ; ^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 of its mother. Such provisicm 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 during 



1 



