S04 Trans. Acad. Sci. of St. Louis, 



plane of the section, as is indicated by the dotted line c?, which 

 is intended to show that the cytoplasm at that point is but 

 slightly below the plane of the section. A comparison of 

 this with s, figure 4, and with figure 4a shows at once that 

 the portion appearing now as non-nuclear, and in this case 

 connected directly with the nuclear portion, is several times 

 greater than the cytoplasmic forward end of the free swim- 

 ing spermatozoid. But one interpretation seems to be 

 admissible — that when the nuclear portion has forced 

 an entrance into the egg-nucleus it breaks out of its cyto- 

 plasmic envelope and slips into the nucleus of the egg, leaving 

 the empty envelope behind in the cytoplasm. This agrees 

 with the statement of Ikeno for Cycas — *' Sofort nach sei- 

 nemEindringen in die Eizelle schliipft das Spermatozoid aus sei- 

 nem Cytoplasmamantel, welcher sich bald innerhalb der Eizelle 

 desorganisirt, wahrend gleichzeitig der Spermakern nach dem 

 Eikerne sich hinbewegt " (p. 595). In the fern, however, the 

 cytoplasmic mantle, having the spiral form of the spermato- 

 zoid, can be more easily identified, to the last. It contains less 

 cytoplasm than that of Cycas, consequently fits the nuclear 

 portion more closely, so that it is carried further into the egg, 

 while in Cycas it is left (Ikeno, fig. 35) at the periphery 

 of the egg. Here it is carried as far as the nuclear membrane 

 ordinarily, and in this one case I find it was drawn partly 

 inside before the nucleus finally escaped. Figure 13a repre- 

 sents in a somewhat diagrammatic way the same nucleus as 

 figure 13, leaving out details in shape, and turned on a verti- 

 cal axis as x-y about ninety degrees. In this figure the fun- 

 nel-like depression d lies in the upper surface a little on one 

 side of the center. Its edge is much higher on one side 

 than on the other. In fact this depression, to which the name 

 ** receptive spot" has often been applied, is no more regular 

 in shape and position than the outline of the nucleus. Its oc- 

 currence is due to the fact that the nucleus conforms itself 

 in a general way to the shape of the cell. The depression 

 occurs in the surface of the cell, and the nucleus, having the 

 peculiar amoeboid form, naturally shows the same depres- 

 sion. The spermatozoid coiled in this receptive spot 

 broke through the nuclear membrane at the point e just 



