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T. AIDA. 



absorbed into tbe ovum to wbicb they are attached, until the latter has fully 

 grown. Often we see these cells arranged under an ovum like a stair, 

 fig. 5, as Gkassi found in the young ovum of some species [Sag it ta 

 Claparedi). I was unable to find a stalk cell with such a long tail-like 

 portion as Grassi describes ; all the stalk cells of our specimens of 

 Sagitta bipnnctata, Sagitta enfiata, Sagitta aerratodentata, etc. are 

 round or rectangular. 



The ova, which have no follicle, must take their nutriment from, or 

 through, these stalk-cells. I am inclined to believe that the stalk-cells 

 do not merely serve as food materials to the ova, but that they in some 

 manner perform the function of actively nourishing the ova, as a follicle or 

 a nutritive cell does, and that when they lose their capacity for that func- 

 tion are merged into the ovum at whose base they lie, andare replaced by 

 the next cell. When all the stalk cells derived from a single epithelial cell 

 are taken up, others will be produced from a neighboring cell to nourish 

 the same ovum to its maturation. Thus as the cells of the germinal 

 epithelium are constantly taken up by an ovum, there is necessarily formed 

 an interruption in the epithelium directly under the ovum, and this inter- 

 ruption becomes the wider, the greater the number of cells taken up. 



The last one of the stalk-cells, which is attached to the ripe 

 ovum, is always larger than its predecessors and behaves somewhat dif- 

 ferently from them. It is never fused with the ovum to which it is 

 attached, but remains as a stopper of the interruption in the germinal 

 epithelium (a, fig. 1). It is this stalk-cell which Con.vnt* has described as 

 preceding the ovum in its passage to the temporarily formed oviduct. I 

 must notice here that the deepness of the interruption varies according 

 to the thickness of the germinal epithelium. In animals which have 

 a thin germinal epithelium, e. g. small specimens of Sagitta bipunctata, 

 Sagitta, enfiata, Sagitta 'mini ma, etc., it is so shallow that the enlarged 

 stalk-cell nearly fills it up, and is easily overlooked. 



From certain stages in its development, an ovum shows at its 



* Ann. &■ Ma£. X. at Hist ser. (!. vol. 13, no. 105, 1896 



