The Ovogenesis of Hydra. 309 



7. The increasing- interstitial cells form, at first, an irregular 

 flattened mass which later becomes a plate with roughly parallel 

 sides and convex ends, lying- beneath the ectoderm. 



8. The region is marked, in early stages, by its translucency 

 in contrast to the opacity of the surrounding tissue. 



9. The interstitial cells at the center of the ovary are larger 

 than those at the margin (Text Fig. A and B). My measurements 

 show that the central cells average four times, or a trifle more the 

 volume of the marginal. It is to be remembered that these central 

 cells are adjacent to the growing eggs : the influences causing rapid 

 growth seem to emanate from them. 



Fig-. A. Fig. B. 



Fig. A. A pair of interstitial cells near the margin of the ovary. 1200 : 1. 

 The cells, together, measure 22 a along the long axis of the figure. 



Fig. B. Interstitial cells from near the center of the same ovary. 1200:1. 

 Together, the two cells measure 36 /« along the long axis of the figure. 



10. The interstitial cells come to be arranged in rows converging 

 toward the center where the eggs lie. The radiate appearance of 

 the ovary is often very marked; in the living hydra it is emphasized 

 by the lines of droplets or granules that are moving toward this 

 central spot. The physiological explanation is evident; the cells 

 have lined up to facilitate the transfer of nutritive material to the 

 eggs and to carry the excretory products away from this center of 

 metabolism. 



11. Kleinenbeeg, working largely on H. viridis, and other 

 investigators, working on some other species, state that the %gg 

 appears only after the ovary has achieved considerable size. My 

 studies force the conclusion, however, that the %gg cell or cells are 

 always present, even before the proliferation of the interstitial cells 

 begins the formation of the ovary, and not only present but rapidly 

 growing (see 13, below) (Fig. 3, Plate 11). 



12. The Qgg cell which has lain in the midst of the cells of 



