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98 FECUNDATION } HETEROGAMETES. 
of the cytoplasm just beneath the wall of the oogonium on the side 
nearest the antheridium presents a granular and more homogeneous 
appearance. At this place a papilla with a deeply stained apical spot 
is formed, which tends to bore its way through the wall of the 
oogonium, causing the wall to become thinner. This is called the 
receptive papilla, since it marks the spot at which the conjugation-tube 
penetrates the odgonium. It doubtless facilitates the development of 
the conjugation-tube. 
In A. portulacee (Stevens,’g9) this receptive papilla seems to pene- 
trate the antheridium. 
The differentiation of the odspore, which now begins, is manifested 
in the contraction of the protoplasm toward the center into a rounded 
mass connected with the wall of the odgonium by thick plasmic 
strands. This mass contains all the nuclei (Fig. 35,C). It gradually 
becomes further differentiated into a central vacuolate and reticulate 
mass, the ooplasm, which becomes the egg-cell or oosphere, and an 
exterior layer of very dense non-vacuolate cytoplasm, the periplasm. 
With the exception of a few plasmic strands, which extend to the wall 
of the oogonium, the entire protoplasmic contents outside the odsphere 
become finally condensed into periplasm. The nuclei, located mostly 
in the periplasm and gradually becoming more and more restricted to 
this layer, now undergo karyokinetic division whereby their number is 
doubled. Stevens claims that two mitoses occur in both sexual organs 
during their development. 
While nuclear division is taking place a dense granular and rather 
sharply defined mass of cytoplasm appears in the center of the not yet 
completely differentiated odsphere (Fig. 35, C,@). Wager, ’96, says: 
It is of the same nature as the densé protoplasmic mass which appears in the 
fertilizing tube at the moment when it begins to grow, and is produced probably 
by an accumulation of stainable granules from the protoplasm. This dense 
mass of protoplasm can be observed in odgonia of all stages, such as are figured 
in (1. c.) Figs. 8 and 22. Shortly after its appearance one of the nuclei produced 
by the division in the oogonium comes into close contact with it, and gradually 
becomes more or less completely embedded in it. All the other nuclei pass to 
the periplasm, leaving this single nucleus in the center as the nucleus of the 
ovum (Fig. 35, D, E). 
At this stage the odsphere may be consideréd as differentiated, 
although its limiting plasma membrane has not yet appeared. 
It seems that this central cytoplasmic body or mass which has 
received much attention at the hands of later observers was described 
by Dangeard as an oil globule, and mistaken by Chmielewskij for a 
