OVUM. 



2nd. In Animals known to be capable of 

 s-xuul generation ; including two varieties, viz. 



a. Multiplication of similar individuals, 

 either in a mature or immature condition. 



I). Multiplication of individuals, generally 

 dissimilar from those producing them, and 

 becoming at last mature or complete in the 

 exercise of the true generative function. 



Some account of these various forms of the 

 reproductive process, and especially of the 

 last, as established by recent discovery, sup- 

 plementary to that contained in the Article 

 GENERATION, may be introduced here, with a 

 view to serve as a foundation for general 

 views of the nature of the ovum, and its 

 relation to the reproductive process in ge- 

 neral. 



I. OF THE OVUM IN GENERAL, AS RELATED 

 TO THE SEXUAL PROCESS OF GENERATION. 



The term orum is in this article entirely 

 restricted to the product of sexual genera- 

 tion. This body is formed in the ovary of the 

 female parent (or in the female organ of a 

 hermaphrodite parent) by a graduaf process 

 of growth or development. When it arrives 

 at a state of maturity, it is spontaneously dis- 

 charged from the place of its formation, a 

 process which in the higher animals has re- 

 ceived the name of Ovulation. If left to 

 its own unassisted powers, no organic change 

 of importance follows in the ovum, and it 

 remains incapable of producing an embryo. 

 But if, at or near the time when the ovum, in 

 a state of maturity, leaves the ovary, it be sub- 

 jected to the influence of the male product 

 or sperm by the contact of a very minute 

 portion of that substance, it then undergoes 

 the change of Fecundation, by which it has 

 communicated to it the power of having de- 

 veloped within it a new being specifically 

 resembling its parents. 



Although there are many great apparent 

 differences in the form and structure of the 

 ova of animals*, yet a general comparison of 



their organisation shows that they consist in 

 nearly all of parts that are essentially the 

 same. These parts in the ovarian ovum are 

 the following, beginning with that which 

 appears most essential : 1st, The Germinal 

 Vesicle, or Germ-cell; a nucleated organ'c 

 cell of microscopic size, generally situated 

 near the surface of the ripe ovarian ovum : 

 this is embedded superficially in, 2nd, The 

 Vitelhis, Yelk) or Yolk, a mass of oleo-albu- 

 minous matter, partly fluid, and partly 

 cellular and granular, generally of propor- 

 tionally much greater size than the germ-cell, 

 and serving to furnish materials for the 

 changes of that body, and for the develop- 

 ment of the new being. Both of these parts 

 are enclosed by, 3rd, The ViicUine, or Yolk- 

 Membrane, a vesicular, nearly structureless, 

 membrane, which contains the rest, and gives 

 to the whole usually more or less of a sphe- 

 rical form. To the assemblage of these parts, 

 constituting the ovarian ovum, and which may 

 be looked upon as most immediately im- 

 portant in connection with the formative pro- 

 cess, there are generally added, after it has 

 left the ovary, and in the progress of its 

 descent through the female passages, some 

 others, such as the albumen, outer membrane 

 and shell of the bird's egg. In their simplest 

 form these additional parts constitute an ex- 

 ternal covering of the egg, to which the name 

 of Chorion is often applied. 



If the ovum be traced back to its earliest 

 origin in the ovary, it is found to consist at 

 first of the germinal vesicle, germ-cell or its 

 nucleus (Jig. 1, c.). To this cell the sub- 

 stance of the yolk is added in the progress of 

 its formation, generally in a gradual manner, 

 but in some animals more suddenly. 



Fig. 2. 





Ovarian Ovum of a Klammifer. 

 a, entire ; 6, burst, showing 1 the germ-cell, with 

 yolk granules flowing out of the vitelline membrane ; 

 c, the ovarian ovum at an early stage of its formation, 

 consisting of the germ-celf surrounded by a few 

 yolk granules. 



* The most important of these will be noticed in 

 ft later part of the article. 



Spermatic Filaments (From P. Wagner and 



LeuchliardC). 

 a, spermatozoa of the squirrel. 

 6, spermatozoa of the dog, in the interior of the 

 developing cell. 



The Spermatic Substance, or Sperm of the 

 male, when examined in its state of maturity, 

 as it is applied to the ovum, and effects in it 

 the peculiar change of fecundation, is observed 

 to consist essentially of an immense number of 

 minute bodies, generally consisting of a 

 thicker particle, with a fine filament attached, 



B 2 



