The Ovogenesis of Hydra. 315 



The tests which have determined this are two. l^t Animals with 

 ovaries killed with osmic acid are preserved in a fluid containing 

 potassium bichromate, such as Mekkel's or Müller's fluid. When 

 treated with an iron alum solution the j'olk granules then stain 

 intensely; but if the sections are stained without such treatment 

 the yolk remains unstained (compare Fig. 6 and 7, Plate 11). This 

 property of staining after osmic and potassium bichromate only 

 Avhen treated with iron alum is characteristic of lecithin (Lee, 

 3Iicroscopists' Vade-mecum, 6tli Ed.). This test was hit upon 

 accidentally; in trying various methods of preserving and staining 

 to get, if possible, some method which would obviate the intense 

 blackening of the yolk and consequent opacity of the egg sections, 

 it was found that material killed in osmic-MEECKEL and stained with 

 gentian violet showed the egg nucleus unobscured by the yolk 

 granules. The significance of the fact was not realized until later 

 when the second test was also applied, namely, 2i«l the Marche 

 test for lecithin, as follows: The hydras are killed in osmic acid 

 and left in it for several minutes; they are then hardened in a 

 potassium bichromate solution, sectioned and mounted, when the 

 yolk granules will appear black. If, however, the animals are 

 killed in a potassium bichromate solution (Müllee's fluid, hot) and 

 then put into the osmic acid for a few minutes, hardened in alcohol, 

 sectioned and mounted, the yolk granules are not evident. 



Kleinenberg attempted to make some chemical tests on the 

 content of the pseudocells in H. viridis; he concludes that they 

 contain a few fat particles but mostly proteid granules floating in 

 a watery fluid in their interior, while the peripheral portion is a 

 sort of plasma. Korotneff concluded that the pseudocells are 

 nuclei because they stain so intensely with the nuclear stains; 

 others, again, have considered them fatty in nature because they 

 blacken with the osmic acid. In an earlier paper, I concluded that 

 the granules which one observes in the ectoderm and endoderm 

 cells during spermatogenesis, are fatty because of this staining 

 reaction with osmic acid. These granules come to lie in numbers 

 at the peripheral ends of the ectoderm cells in well fed hydras 

 (Fig. 3, Plate 11); they give the brown color to the three brown 

 species and seem to be especially abundant in the reproducing 

 animals. More careful tests show that neither these granules nor 

 the pseudocells are fat; in fresh material stained with Sudan III, 

 a specific fat test, they do not take up the color. In fact such tests 



