The Ovogenesis of Hydra. 317 



size until the egg has achieved considerable size, perhaps an eighth 

 of its adult volume. 



21. The ectoderm cells are greatly altered in the region of the 

 ovary. Their outer ends are transformed into lamellae which are 

 united by their edges to form the covering of the eggs: their bodies 

 form muscular fibres which are crowded to the sides by the egg 

 like the restraining guy-ropes about an inflating baloon (Fig. 11, 

 Plate 12). 



22. When the formation of pseudocells is complete, in other 

 words when the egg has stored sufficient yolk, the pseudopodia are 

 withdrawn. The egg becomes spherical to ovoid with the narrow 

 end pointed centrad. 



23. The nucleus, which has been at its center, moves to the 

 periphery. 



24. As the egg reaches its maximum size, the endoderm cells 

 below it are seen to be more or less filled with excretory matters 

 so that the whole region is darkened. 



25. A fair sized mature egg of //. dioecia measures 0,4 mm in 

 diameter. The nucleus which has grown with great rapidity in the 

 later stages of the egg growth measures 60X45 a and its nucleolus 

 has a diameter of about 13 /<. 



26. The cloud of chromatin which Brauer observed in the 

 neighborhood of the nucleus disappears gradually. It is as if the 

 chromatin formation had been going on with great vigour during 

 this excessive growth of the nucleus so that the region about the 

 nucleus also was charged with the diftuse chromatin material: now 

 a new process sets in. The nucleus becomes finely punctate with 

 particles of chromatin (Fig. 8, Plate 11). The nucleolus becomes 

 lighter at the center but stains intensely at its periphery; a few 

 spherical masses of darkly staining material are left within it. 

 Meanwhile the chromatin points throughout the nucleus are growing 

 plainer: one must conclude, apparently, that the material of the 

 nucleous is passing out into the nucleus to increase the chromatin, 

 leaving only a few masses of residual matter. When this pro- 

 cess is complete, the nucleolus collapses and disappears. There 

 is simultaneously an outrush of fluids from the nucleus, as Brauer 

 observed, driving the yolk granules back from its immediate 

 neighborhood. The region about the nucleus is plainly marked by 

 this clear area (Fig. 8, Plate 11 and Fig. 12, Plate 12). 



27. jMeanwhile the whole egg contracts, emitting a fluid which 



