The Ovogenesis of Hydra. 313 



of the small yolk granules formed by and within the eg'g-; 2. by the 

 ingestion of entire interstitial cells when the nucleus of the ingested 

 cell may become a pseudocell. These pseudocells have given rise 

 to much discussion. Ecker believed them embryonic cells, mistaking 

 the prominent nucleolus, evidently, for the cell nucleus. Kleinenber& 

 thought they appeared in the egg as tiny bodies and then grew by 

 the absorption of nutritive material largely derived from the dis- 

 integration of the neighboring interstitial cells. Koeotneff con- 

 cluded that they are the entire nuclei of these cells ingested by 

 the egg. NUSSBAUM saw such nuclei disintegrating, however, and 

 entering the egg as rows of tiny droplets and unable to harmonize 

 the conflicting statements, left the question open. Brauee later 

 agreed with Kleinenberg; Tannreuther, more recentlj^, coincides 

 with KoEOTNEEE, adding that after ingestion the nuclei continue to 

 divide amitotically. Now I believe that these apparently contra- 

 dictory statements simply deal with different phases of one and the 

 same process. At first the egg is nourished exactly as are the 

 adjacent ectoderm and interstitial cells; material elaborated by the 

 endoderm cells is passed to them all. The egg holds this material 

 diffused throughout it, in the beginning, but later it appears, pro- 

 bably somewhat altered, in granules: these coalesce and make the 

 pseudocells (Fig. 3, Plate 1 and Fig. 6, Plate 11). The same material 

 is taken up by the interstitial cells; it is transformed by them 

 and stored in the nucleus (Fig. 10, Plate 11). If now this trans- 

 formation is complete when the cell is ingested by the egg the 

 nucleus becomes at once a pseudocell; if, however the process is 

 incomplete, the egg must disintegrate the nucleus in order to com- 

 plete the transformation of its substance into yolk. Attention is 

 called to Fig. 3, which shows a typical condition during the growth 

 of the egg. The nuclei of the endoderm cells are usually at the 

 mesogloeal ends; the ectoderm nuclei, on the contrary, are at the 

 outer ends of the cells away from the mesogloea. The ends of the 

 ectoderm cells adjacent to the mesogloea appear filled with threads 

 and stain lightly while the opposite ends are full of deeply staining 

 granules. There are, then, two types of procedure when the egg 

 appropriates the interstitial cells; first, when the interstitial has 

 failed to complete its elaboration of the required yolk ; second, when 

 the interstitial has completed this process. 



The first type has been so well described by Nüssbaum that 

 I can not do better than freely translate his words; he says: "The 



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