The Ovogenesis of Hydra. 305 



rest of the space is filled with a water clear fluid through which 

 streams of plasma pass. About the time that the formation of the 

 pseudozellen ceases a great change occurs in the nucleus. It has 

 heretofore lain at the center of the egg but now it takes an eccentric 

 position, finall}' coming to lie at the periphery of the egg, at its 

 outer pole where it is covered only by a very thin layer of proto- 

 plasm. A degeneration occurs within it: the granules dissolve and 

 a part of the fluid is squeezed out of the membrane so that the 

 nuclear wall collapses. Fatty degeneration is apparently occuring. 

 the Proteids changing to fats; what becomes of the membrane is 

 not clear: at any rate before fertilization occurs the whole nucleus 

 has disappeared." 



"When the egg has about reached its maximum size, the endo- 

 derm cells below it are filled with excretory products so that the 

 whole region is almost black, evidence of the intense metabolism 

 that has been going on at this point. The growth of the ovary 

 does not continue long after the egg appears, its cells no longer 

 multiply; the smaller ones at the periphery grow larger, then they 

 shrink a trifle, the plasma becomes glassy, the nucleus irregular 

 fat droplets appear abundantly and finally the cells disintegrate to 

 form nutritive material for the egg. The outer layer of the ecto- 

 derm which covers the ovary suffers only passive alterations, as it 

 is pushed up so as to form a sack by the growing egg. The cells 

 are transformed into lamellae at their peripheral ends but the 

 connection is still maintained with the muscle fibre of the mesogloea 

 so that the cells are greatly elongated and pass about the egg; 

 the cells are thus at times "2 mm in length." 



•'Shortly after the disappearance of the nucleus the egg contracts, 

 emits a not inconsiderable quantity of water-clear fluid which 

 spreads out between the egg's surface and its ectodermal sheath, 

 Eegularly, too, there are pressed out a pair of tiny bits of the egg 

 substance; they are either held in the sheath or else they lie clear 

 in the space filled with the fluid: these are the polar bodies. 

 The fluid escapes from a small orifice formed between the ectodermal 

 cells at the apex of the ovary: shortly afterwards the ectodermal 

 cover of the egg contracts and the egg is squeezed out through the 

 orifice. At first a tiny bit of the egg protoplasm protrudes, then 

 more, like a papilla. The egg content flows into this rapidly and 

 an hour glass stage is reached, half the egg within and half outside 

 the narrow opening. Finally the egg is all pressed out except a 



