84 



as a delicate layer, composed of minute protoplasmic granules, 

 on the inner side of the periplasmic layer and just outside the 

 central space and its small quantity of protoplasm and nuclei 

 (Fig. X. o). This granular layer is probably derived from the 

 periplasm. By the complete fusion of these granules with one 

 another a delicate hyaline membrane is formed (Fig. XI. o), the 

 cell-wall of the oosphere. This wall gradually increases in thickness 

 by the addition of new layers to its exterior, which are derived 

 also from the periplasm. The nuclei of the periplasm are at 

 this stage dividing up rapidly, so far as can be seen, by a 

 process of karyokinesis, into a lai'ge number of very small 

 nuclei, and these are gradually transformed into layers forming 

 the outer cell wall of the oospore. These periplasmic nuclei 

 thus seem to have a very distinct function ; forming as they 

 do a large part of the material out of which the cell wall is 

 built up. 



At the time wlien the nuclei are arranged regularly in 

 the peripheral protoplasm of the oogonium the antheridium 

 begins to develop a fertilising tube which penetrates the 

 oogonium, and increases in length until it comes in contact with 

 the oosphere, just at the time when the cell wall of the latter 

 is formed (Figs. X. and XI.). The antheridial tube is much 

 elongated, and does not pass directly to the oosphere, but takes 

 a somewhat oblique course to one side of it. The end of the 

 tube is swollen in a characteristic manner. The swelling is 

 cylindrical and takes up about one-third of the length of the 

 tube. It is this portion of the tube wliich conies into close 

 contact with the wall of the oosphere. In two cases, at least, 

 I have been able to observe an opening between the terminal 

 portion of this swelling and the oosphere (Fig. XII. f) ; this 

 opening, however, is extremely small and easily overlooked. 



The antheridium contains at this period a large number of 

 small nuclei which have been derived from the division of the 

 pre-existing larger nuclei (Fig. XII.). One or more of these 

 nuclei pass over into the fertilising tube together with a small 

 quantity of protoplasm (Fig. XI.). The oosphere at this stage 

 contains one nucleus, which exists in place of the two or more 

 pre-existing nuclei, these having fused togetlier to form the 

 single central nucleus ; at a later stage, however, two nuclei are 

 to be observed (Fig. XII. n), and at a still later stage a single 



