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 oogonium. It doubtless facilitates the development of 

 the conjugation-tube. 



In A. portulacece (Stevens, '99) this receptive papilla seems to pene- 

 trate the antheridium. 



The differentiation of the oospore, which now begins, is manifested 

 in the contraction of the protoplasm toward the center into a rounded 

 mass connected with the wall of the oogonium 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 oosphere 

 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 oosphere (Fig. 35, C, a). Wager, '96, says : 



It is of the same nature as the dense 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 oogonia 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 oosphere may be considered 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 



