The Ovogenesis of Hydra. 307 



"In the nucleus of the young- egg- are found, besides its bounding 

 membrane, a large nucleolus, a reticulum of achromatic fibers and 

 chromatin particles and the nuclear sap. The nucleolus of the egg 

 grows by fusing with other smaller nucleoli which are constantly 

 being- formed. The achromatic net constantly becomes finer meshed 

 so that during growth all but the nodal points disappear. The 

 chromatin, however aggregates in the neighborhood of the enlarging 

 nucleolus; in this spot the chromosomes ultimately appear, apparently 

 forming from this chromatin mass. The achromatic part of the 

 maturation spindle is formed from the achromatic net- work. The 

 approach of the maturation is marked by an outflow of clear nuclear 

 sap which pushes back the pseudozellen from the neighborhood of 

 the nucleus; by a partial collapse of the nuclear wall and by the 

 rapid disintegration of the great nucleolus. The achromatic net- 

 work now becomes apparent again. A part of the nucleolus dissolves 

 in the nucleus, a part is given off into the cell body. The hydra 

 egg consists of a central mass full of pseudozellen and an outer 

 rind of protoplasm which is thickened decidedly at the spot where 

 the polar bodies appear, where the nucleus continues to lie and 

 where the cleavage appears. The maturation spindle is barrel- 

 shaped, possesses no polar fibers and contains twelve to fourteen 

 short, rod-shaped chromosomes. The formation of the polar bodies 

 is in the typical manner. The chromosomes apparently divide by a 

 cross division; the nucleus does not go into a rest stage between 

 the formation of the first and second polar bodies. The number of 

 polar bodies is two: the first one does not divide. After the 

 formation of the polar bodies the chromatin remaining is in the 

 tiny nucleus; this grows rapidly, the chromatin dividing and sub- 

 dividing until it is unrecognizable: later the nucleoli appear. The 

 egg pronucleus remains near the surface awaiting the entrance ot 

 the male pronucleus: it lies at the bottom of the depression before 

 mentioned with only the thinnest film of protoplasm above it." 



We may now consider the above joint description, point by 

 point, discussing them when necessary and adding such new facts 

 as I have been able to attain. 



1. The ovaries appear as moundlike protuberances upon the 

 body of hydra (Fig. 1, Plate 11). The question of the order of their 

 appearance is left open for reasons already given. 



2. The ovary may occupy a semicircumference of the animal in 

 H. viridis; in the other species they may be even more extensive. 



