310 Trans. Acad. Sci. of St. Louis. 



the spindle. This figure may then be regarded as represent- 

 ing the earliest indications of the first division spindle in the 

 embryo and the process of fertilization must be regarded as 

 completed. 



Although in the course of this investigation I have sectioned 

 many embryos, I have not yet attempted to carry my investi- 

 gation further into the details of the formation of the embryo 

 itself. 



The observations above and a consideration of my figures 

 give convincinsr evidence that the course of fertilization in 

 Aspidmm and Adiantum at least, and probably in many other 

 ferns, differs greatly from the generally accepted description. 

 The entrance of an unchanged sperm-nucleus into the egg 

 nucleus has been described already by Shaw for Onoclea and 

 Ikeno for Cycas. Shaw has found the spermatozoid enter- 

 ing the egg-cytoplasm. He has figured the sperm-nucleus 

 within the eofg-nucleus. I have been able to show the un- 

 changed spermatozoid as it lies coiled in the depression in the 

 surface of the cell and to trace it into the cytoplasm of the 

 egg, through the nuclear membrane, to the actual mixing of 

 the chromatin of spermatozoid and egg. I have shown 

 that the entire sperm-nucleus slips out of the cytoplasmic en- 

 velope, or mantle (to use Ikeno's term), just as it reaches the 

 nuclear membrane of the egg, so that it passes directly from 

 its own cytoplasmic sheath into the egg nucleus. In Cycas it 

 appears to leave its cytoplasm near the periphery of the egg. 

 The nucleus of the spermatozoid carries in with it other mate- 

 rial besides chromatin. This material forms the central 

 mass, and is surrounded by the chromatin. Such a conclu- 

 sion agrees with the ordinarily accepted views of fertilization 

 more closely than with the conclusions of Ikeno. The whole 

 nuclear portion of the spermatozoid here enters the nucleus 

 directly. In the fertilization figures for animals such as 

 Nereis (Wilson, p. 141) we find that the sperm-nucleus has 

 swollen and assumed all the characters of an ordinary nu- 

 cleus, so that the gametes are equal, not only qualitatively 

 but quantitatively, at the time of fusion. In the phanero- 

 gams, as far as described, we never find these changes in 

 structure in the generative nucleus of the pollen-tube which 



