THE OVUM. 



45 



J'c 



FIG. 1 6. FOLLICLE OK 

 BONELLIA AT A MEDIUM 

 STAGE OF DEVELOPMENT. 

 (After Spengel.) 



m>. ovum. fe. flattened 

 follicular epithelium. 



the character of its nucleus. The remainder of the larger cells 

 become of the same size as their neighbours. The ovum now 

 becomes more or less separate from the mass of germinal cells, 

 rapidly grows in size, and soon forms the most considerable 

 constituent of the follicle (fig. 16, ov}. The 

 remaining germinal cells are quite passive, 

 and though, with the exception of the 

 central cell, they do not appear to atrophy, 

 they soon constitute a relatively small 

 prominence on the surface of the ovum. 

 By the rupture of the stalk the whole 

 follicle becomes eventually detached, and 

 the further development of the ovum takes 

 place in the body cavity. A vitelline 

 membrane is formed, and eventually the 

 ovum is taken into the oviduct (segmental 

 organ). At this time or slightly before, 

 the follicle cells together with the germinal mass, which through- 

 out exhibits no signs of atrophy, become thrown off, and the 

 ovum is left invested in its vitelline membrane. 



NEMATOUA. 



(44) Ed. Claparede. De la formation et de la fccondation des ceufs chez les Vers 

 Nematodes. Geneve, 1859. 



(45) R. Leuckart. Die menschlicJien Parasiten. 



(46) H. Munk. " Ueb. Ei- u. Samenbildung u. Befruchtung L>. d. Nematoden." 

 Zeit. f. wiss. Zool., Vol. ix. 1858. 



(47) H. Nelson. " On the reproduction of Ascaris mystax, etc." Phil. Trans. 

 1852. 



(48) A.Schneider. Monographic d. Nematoden. Berlin, 1866. 



The female organs consist as a rule of two caecal tubes which 

 unite before opening to the exterior. Each of these is divided 

 into a vagina, uterus, oviduct, and ovary. The ovary constitutes 

 the blind end of the tube, and is formed of a common protoplas- 

 mic column, holding a number of nuclei in suspension. The 

 protoplasm becomes cleft around the nuclei in the uppermost 

 part of the tube ; the circumscription of the ova proceeds, how- 

 ever, very gradually, and since it commences at the periphery 

 of the column the ova remain attached by stalks to a central 

 axis with one end free. In this way there is formed a rod-like 



