36 NEMATODA. 



attached by a stalk to the peritoneum. The central cell of each mass 

 grows larger than the rest, which arrange themselves in a columnar 

 fashion round it ; it is not, however, destined to become the ovum. 

 On the contrary certain of the other cells adjoining the stalk grow 

 larger, and finally one of these becomes distinguished as the ovurn by 

 its greater size and 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 even- 

 tually 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, STAGE OF DEVELOPMENT. 

 which throughout exhibits no signs of atrophy, (After Speugel.) 



become thrown off, and the ovum is left p. ovum. /?. flattened 



i , , IT i follicular epithelium. 



invested in its vitelline membrane. 



NEMATODA. 



(44) Ed. Claparede. De la formation et de la ficondation des aufs chez les Vers 

 Ngmatodes. Geneve, 1859. 



(45) R. Leuckart. Die menschlichen Parasiten. 



(46) H. Muuk. "Ueb. Ei- u. Samenbildung u. Befruchtnng b. d. Nematoden." 

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



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

 1852. 



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



The female organs consist as a rule of two crecal 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 protoplasmic 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, however, 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 structure known as the rachis, which 

 consists of a central axis with a series of half circumscribed ova 

 radiately arranged round it. In the lowest part of the ovary the ova 

 become completely isolated and form separate cells. 



