348 



SENESCENCE AND REJUVENESCENCE 



Figs. 192-195. — The differentiation of parthenogenic and zygogenic eggs: Fig. 

 192, ovarian tubule o£ Sida (daphnid crustacean), showing primitive germ cells, pc, 

 and groups, g g, of eggs, 0, and nurse cells; Fig. 193, part of a tubule containing a 

 zygogenic egg, 0; Fig. 194, ovarian tubule of Melanoxanlhiim (plant louse), showing 

 nutritive gland, gl, parthenogenic egg, 0, and embryo, em; Fig. 195, ovarian tubule 

 of Melanoxanthum, showing nutritive gland, gl, and zygogenic egg, 0. Figs. 192, 193, 

 from Weismann, '77; Figs. 194, 195, from Tannreuther, '07. 



