270 Wager.—On the Fertilization 
the antheridium becomes very thin and a slight hyaline proto¬ 
plasmic papilla becomes formed which tends to push itself into 
the antheridium (Fig. 1). The same structure occurs in C. can - 
didus , but is more prominent, and in C. Bliti Stevens has 
shown that it is still more highly developed ; for the proto¬ 
plasm pushes itself actually into the antheridium and there 
forms a very conspicuous swollen papilla inside it h 
Whatever may be the exact explanation of this curious 
structure, it appears to be connected in some way with the 
perforation of the oogonial wall and the formation of the 
fertilizing tube. It is much less highly developed in C. can - 
didus and P. parasitica than in C. Bliti . I have called it 
the receptive papilla, because it marks the place where the 
penetration of the fertilizing tube takes place. Stevens is 
inclined to give it a more important significance than this; 
but it appears to me to be distinctly homologous with the 
receptive spot of other ovum-cells and to perform a similar 
function. Such receptive spots or papillae are found in 
the oogonia of Vaucheria and Oedogonium , and are well 
marked differentiations in the protoplasm. 
As soon as the oogonium is formed the nuclei begin to 
increase in size; the linin-network and chromatin-granules 
become more prominent and stain more deeply. The cyto¬ 
plasm loses at the same time, to some extent, its power of 
taking up stains, and the vacuoles become larger and less 
numerous. Then a differentiation of the protoplasm into 
ooplasm and periplasm begins, and all the nuclei pass into 
the periplasm (Fig. 2). They here undergo mitosis. The 
two regions are distinctly marked off from one another, 
although as yet there is no partition-wall between them. 
The periplasm is a granular, homogeneous layer at the peri¬ 
phery of the oogonium. The ooplasm is a vacuolate 
spherical mass of cytoplasm in the centre (Figs. 2, 3, 4). The 
nuclei at this stage are often arranged in a single regular 
layer immediately around the periphery of the ooplasm 2 . 
1 loc. cit. p. 154 (see Plate XIII, Figs. 47-54). 
3 See Fig. 8, Plate VI, Ann. of Bot., vol. iv, 1889. 
