i 9 o8] YAMANOUCHI—SPERMATOGENESIS AND OOGENESIS 149 



brane around the fertilized egg within a very few minutes after the 

 entrance of the sperm, while Shaw in his paper (79) on Onoclea found 

 no evidence that a membrane of appreciable thickness was formed 

 immediately after the entrance of sperm. 



In his account of Adiantum and Aspidium, Thom finds that when 

 the sperm reaches the nuclear membrane, the nuclear part of the sperm 

 finds or breaks an opening into the egg nucleus and cytoplasmic 

 envelope, while the blepharoplast and the cilia are left out in the cyto- 

 plasm of the egg. Whether blepharoplast and cilia are left out in the 

 cytoplasm Shaw leaves in doubt. 



That the egg nucleus during the entire process of fertilization is in 

 the resting condition and that the sperm enters the egg nucleus before 

 undergoing any change in form or visible structure, are points of 

 agreement among these authors in their studies on Adiantum, Aspid- 

 ium, Onoclea, and Osmunda. One peculiar case, different from the 

 foregoing results, was reported for Pilularia by Campbell (13), who 

 finds that a sperm nucleus assumes a loose and more granular struc- 

 ture and rounds up before entering to unite with the nucleus of the egg. 



No work has been published showing details of the behavior of 

 chromosomes during spermatogenesis, oogenesis, and fertilization in 

 pteridophytes, ncr has the organization of the figure of first segmenta- 

 tion division ever been followed. 



The present investigation of this subject, with a study of sporo- 

 genesis which was considered in my recent paper (101), was carried on 

 to trace out the complete history of the chromosomes throughout the 

 life-cycle of Nephrodium molle Desv. The former paper, together 

 with the present investigation, may serve as an introduction to the 

 study of apogamy in Nephrodium, which will appear in a subsequent 

 paper. 



Material and methods 



Gametogenesis and fertilization were studied from prothallia raised 

 from spores in the greenhouse of the Hull Botanical Laboratory during 

 the five months beginning October 1906. The spores for this culture 

 were collected from leaves of the same individuals of Nephrodium 

 molle that furnished material for the study of sporogenesis. 



Various fluids were used for killing and fixing. The best fixation 

 for the present studies was obtained in the material killed and fixed in 



