310 Elliot R. Dowxixg. 



tlie ovaiy becomes conspicuous because of its rapidly increasing- size, 

 its elong-ating- form and increasingly irregular contour. 



13. So far as I can find, all investigators, beginning with 

 IvLEiNENBEEG, have maintained that the egg is merely an interstitial 

 cell which, after the ovary has begun to grow^, increases in size 

 more rapidly than its fellows and assumes new characters. From 

 such unanimity of opinion I hesitate to dissent but in my sections 

 through hundreds of ovaries the egg cells are always distinct, even 

 in early stages, and are derived, in adult life, only from previously' 

 existing, similar cells. I submit the opinion, therefore, that in the 

 adult hydra the oogonia (and spermatogonia) are distinctly 

 differentiated a selfpropagating tissue. These early egg cells are 

 slightly larger than the inactive interstitials and have a larger 

 nucleus in proportion to the cell body. The cell outline is spherical 

 whereas the interstitials are polygonal in outline. Adjacent to the 

 nucleus is a small dark ovoid body which stains deeply with gentian 

 violet. There alwaj^s appears later and frequently at this early 

 stage, a vacuole near the nucleus. The evidence on which I base 

 my conclusion is: 1. That cells with these characteristics are 

 frequently found in mitosis at the point where an ovary is forming. 

 2. That all gradations from the large undoubted egg to this cell 

 are readily found; but intermediate stages between it and the 

 interstitials are not found. Fig. 4 and 5, Plate 11, show the earlj' 

 oogonia among the ectoderm cells. 



We know of many cases among the hydroids in which the 

 ovary is made up of a mass of oogonia one of which changes to 

 the definite egg w^hile the others are used as nutrition for its 

 continued growth. Thus in Pew/aria, Goette tells us (p. 50): "The 

 egg cells multiply extraordinarily and build the principal mass of 

 the ovary on whose suiface there is differentiated a thin epithelial 

 covering. Later a few of tlie young egg cells grow to definitive 

 eggs while the others function as nutritive cells. In the same 

 organ, then, where the eggs are growing the nutritive cells are 

 diminishing in number and that not entirely by atrophy; in unripe 

 eggs there appear entire, ingested nutritive cells." 



Nor is such derivation of the eggs and nutritive cells from the 

 oogonia during adult life confined to the hydroids or even to the 

 lower groups of animals. Giardixa's well known case of the origin 

 of the eggs and nutritive cells in Dytiscus is a case to the point. 

 However, in all groups, I think, where we know of such common 



