THE NUTRITION OF THE OVUM OF HYDRA VIRIDIs. 527 



The greatly enlarged nuclei, gorged with lecithin, also become 

 yolk granules or "Pseudozellen," p. 66. Tannreuther (08) also 

 looks upon the yolk granules as arising from the nuclei of the 

 interstitial cells. He says: "When the pseudopoclia are com- 

 pletely formed, the nuclei of the interstitial cells forming the 

 ovary are taken up by the amoeboid egg and become changed 

 into the yolk or pseudo-cells of the egg. . . . After the yolk or 

 pseudo-cells are formed they divide amitotically" (p. 264). 



We have been unable to bring the details of Hydra viridis 

 ovary in line with the above interpretations and facts. 



To begin with, up until the time that the growing, amoeboid 

 oogonium has made maximum contact with the mesoglea thus 

 placing it in relation to the endoderm there has been no yolk 

 formation. In the meantime, however, many of the attending, 

 peripherally disposed cells have disintegrated and have been re- 

 sorbed. Sometimes this disintegration and resorption has gone so 

 far that, before the oogonium has well advanced in growth, the 

 attending cells lie only at its margin (Fig. i). In a typical 

 example, by the time the oogonium has reached its maximum 

 growth, there is but a thin tissue of highly modified epidermis 

 covering its general surface (Fig. 5). In such example, there 

 may yet be disintegrating cells at the tips of the pseudopods or 

 even beyond them. Thus it is to be emphasized that many of 

 the enlarged interstitial cells have disintegrated (perhaps most of 

 them) and have been resorbed during the oogonium's growth. 

 And yet, up until maximum surface contact with the mesoglea 

 has been established, no yolk formation has resulted. It should 

 be further indicated that we have found no enlarged interstitial 

 cells to be taken up bodily by the amoeboid egg-cell. These two 

 features of the nutrition of ovum of Hydra stand in contrast with 

 what Tannreuther (08) describes. He says: "When the egg has 

 reached its grow r th, it is amoeboid in form with the nucleus near 

 the center. The egg at this stage of development contains no 

 yolk, . . . but when pseudopodia are completely formed, the 

 nuclei of the interstitial cells forming the ovary, are taken up by 

 the amoeboid egg and become changed into yolk or pseudo-cells 

 of the egg. Fig. 6 represents a cross-section of several pseudo- 

 podia into which the nuclei of the interstitial cells of the ovary 





