THE OVUM. 45 



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 



, . ,, , , ., A ., ,,. FIG. 16. FOLLICLE OF 



place in the body cavity. A vitellme BONELLIA AT A MEDIUM 



membrane is formed, and eventually the STAGE OF DEVELOPMENT. 



3 (After Spengel.) 



ovum is taken into the oviduct (segmental OIL ovum> f i flattened 

 organ). At this time or slightly before, follicular epithelium, 

 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. 



NEMATODA. 



(44) Ed. C laparede. De la formation et de la fecondation des ceufs chez les Vers 

 Nematodes. Geneve, 1859. 



(45) R. Leuckart. Die mensc/ilichen Parasitcn. 



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

 Zeit.f. wiss. Zoo!., 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 csecal 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 



