580 THE AMERICAN NATURALIST. [VOL. XXXVIII. 



band which lengthens and finally takes the form of a spiral of 

 five or six turns which becomes more or less closely applied to 

 the plasma membrane (Fig. 10 e, blepharoplast in section). The 

 cilia develop as protuberances from the outer surface of the 

 band (Fig. loc and d} and grow through the plasma membrane 

 to the exterior of the cell. The nucleus in the meantime has 

 increased in size until it occupies the greater part of the top 

 shaped sperm (Fig. loe). 



The history of spermatogencsis in Ginko is strikingly parallel 

 to that of the cycads. The chief features were first described 

 by Webber ('97c) and in greater detail by Hirase ('98). The two 

 blepharoplasts appear de novo on opposite sides of the nucleus 

 in the body cell. They show the same high state of differentia- 

 tion as those of the cycads, being large and the center of a 

 number of prominent radiations. Ginko however presents a 

 peculiarity not reported in the previous group. A large spheri- 

 cal body lies between each blepharoplast and the nucleus in an 

 area of granular cytoplasm. This structure stains deeply like 

 the globules of nucleolar substance which are frequently found 

 in the cytoplasm after nuclear division. They are probably 

 accumulations of a somewhat similar material at these points in 

 the cell to be utilized at later periods of spermatogenesis, since 

 they decrease in size as the sperms mature. The spindle in the 

 body cell is formed between the blepharoplasts but its poles lie 

 at some distance from and are entirely independent of these 

 structures. During this mitosis the spherical bodies pass to 

 one side of the spindle so that the daughter nuclei (sperm 

 nuclei) finally take the position formerly occupied by them. 

 The blepharoplast becomes granular and begins to lengthen into 

 a band, one end of which becomes attached to the nucleus that 

 puts forth a small papilla towards the blepharoplast. The band 

 elongates and takes the form of a spiral which makes several 

 turns around one end of the cell just under the plasma mem- 

 brane. Cilia then develop along this band as in the cycads. 

 The earlier accounts, describing a short tail on the sperm were 

 founded upon material that was not altogether normal and have 

 been corrected by Webber and Fujii. The mature sperms have 

 essentially the same form as those of Zamia and Cycas. 



