Thorn — Fertilization in Aspidium and Adiantum. 309 



fibrous material which seems to come directly from the central 

 mass of the spermatozoid. While the evidence is not con- 

 clusive, the presence of a comparatively large amount of kino- 

 plasmic material in the ordinary nucleus is good ground for 

 expecting to find it here in some form. The active movement 

 of the nuclear portion while the ripe spermatozoid swims 

 through the water would call for the presence of such ma- 

 terial. Its ability to move itself while enterincj the esfor 

 nucleus without the assistance of cilia or cytoplasmic materials 

 points toward the same conclusion. Further, as noticed be- 

 fore, if we compare the chromatin matter as found in the egg 

 in such figures as we have here, with the whole mass of the 

 spermatozoid nucleus regarded as " homogeneous chromatin," 

 the spermatozoid would carry in with it a great preponderance 

 of chromatin. There certainly is no such extrusion of non- 

 chromatin in material from the sperm-nucleus as Ikeno has 

 figured for Cycas revoluta. Whether Ikeno is corrector not, 

 in claiming that only chromatin is essential in fertilization, we 

 certainly have here much other material carried into the egg- 

 nucleus. The entire nuclear portion of the spermatozoid enters 

 bodily into the nucleus of the egg without (here my observa- 

 tions agree with Ikeno for Cycas) increasing the size of the egg 

 nucleus to any appreciable extent. The resulting segmentation 

 nucleus shows no increase in size, but does present a doubling 

 of the quantity of its chromatin. Only that portion of the 

 spermatozoid which comes to lie inside of the nucleus of the 

 egg is known to have any function in fertilization, in forms 

 which like the ferns have no centrosome. Whatever its value 

 may be, the cytoplasmic portion of the spermatozoid is 

 absorbed in the cytoplasm of the egg and its effects cannot be 

 traced. 



The segmentation nucleus gradually loses its irregular con- 

 tour and begins to assume an elliptical outline (fig. 26). 

 The depressions in the surface of the cell and nucleus disap- 

 pear. The cytoplasm usually shows a more markedly radiate 

 arrangement outward from the nucleus. In the same figure 

 (fig. 26) I find in the cytoplasm fibers running from the 

 nuclear membrane toward the periphery of the cell which 

 correspond in course and staining capacity with the fibers of 



