Fecundation of the Ovum. 30^ 



secondary cells are set free. They are frequently distributed on 

 the surface of a sphere of albumen, as is the case in the Anne- 

 lida and Gasteropoda; for these cells are merely the parent- 

 cells [Entwickelungszellen) of the spermatozoa. We shall not 

 follow the further development of the spermatozoa, as its interest 

 here is but secondary, and we shall pass at once to the formation 

 of the ova. The generative organs of the female, like those of 

 the male, are composed of a simple tube or vessel, in which, 

 starting from the csecal extremity, Meissner distinguishes differ- 

 ent parts under the names oi germigene [Eierkeimstock), vitello- 

 gene {Dotterstock), alhuminogene (Eiweissschlauch) , oviduct and 

 uterus. Microscopically, the germigene is exactly similar to the 

 testicle, and contains perfectly diaphanous cells with nuclei and 

 nucleoles. These are the female germ-cells, which present no 

 difference from those of the male. The nucleus of each of these 

 cells divides into two, then into four, eight, &c., but there is no 

 simultaneous division of the nucleole. At this point begins the 

 differentiation of the male and female generative organs. At the 

 bottom of the germigene the nuclei approach the wall of the cell 

 containing them and push it before them, forming sacs into 

 which the contents of the cell penetrate, and which by the 

 gradual constriction of their base at last form secondary cells 

 attached by a peduncle to the primary cell. These secondary 

 cells are the future eggs, produced by a sort of exogenous gene- 

 ration of the female germ-cell. At this moment this bunch of 

 cells passes into the vitellogene, the germ-cell or primary cell 

 being in the centre, and the ova suspended like pears at its cir- 

 cumference by means of hollow peduncles. The vitellogene is 

 perfectly passive, that is to say, it does not secrete the substance 

 of the vitellus. This is produced in the germ-cell itself, and 

 penetrates through the peduncles into the secondary cells, that 

 is to say, into the ova. The membrane of the secondary cells 

 thus becomes a vitelline membrane ; and the nucleus becomes 

 the germinal vesicle with its characteristic spot. The bunches 

 of ova are placed one behind the other in the vitellogene in such 

 a manner that the germ-cells always occupy the centre and the 

 ova the periphery. The consequence of this arrangement is the 

 formation of an apparent axis in the centre of the vitellogene, an 

 appearance which is owing to the succession of the germ-cells ; 

 to this Meissner gives the name of rachis or raphe. At the 

 moment of their entrance into the alhuminogene the ova detach 

 themselves from the germ-cell, and the dehiscence always takes 

 place at the base of the peduncle, which remains attached to the 

 ovum. The ova then become surrounded with albumen. 



Meissner did not turn his attention particularly to the fecun- 

 dation ; but, nevertheless, — and this renders his observations of 



