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THE AMEBIC AN NATURALIST [Vol. XLIV 



Cordaitales had swimming sperms, and further, that 

 they had no- pollen tubes, the pollen grains reaching the 

 female gametophyte directly, then discharging their 

 sperms about as in the living heterosporous Pterido- 

 phytes. 



Definite knowledge of the structure of the sperm be- 

 gins with the cycads, where the sperms are so large that 

 they are easily visible to the naked eye. Broadly speak- 

 ing, their development is like that of most pterido- 

 phytes. In the most thoroughly investigated fern, after 

 the spermatogenous divisions have ceased, two ble- 

 pharoplasts appear in each cell, which then divides so 

 that each of the two resulting cells contains one nucleus 

 and one blepharoplast. From the blepharoplast there 

 is developed a more or less spiral baud which gives rise 

 to numerous cilia. 



In gymnosperms, with the exception of Microcycas, 

 Cupressus and occasionally, Ceratozauiia, no spermatog- 

 enous divisions precede the formation of the cell which 

 is to produce the pair of sperms, and in these three 

 genera it is not known whether the blepharoplast ap- 

 pears any earlier than in the pteridophytes. I suspect 

 that it does not, but it is certain that in the cycads and 

 in (luihf/o two blephai-oplasts always appear in the body 

 cell which is to produce the pair of sperms, and while 

 the blepharoplasts are at first very inconspicuous, they 

 finally become larger than the nuclei of most angio- 

 sperms. 



The mature sperm of the cycad consists of a very 

 large nucleus surrounded by a thin layer of cytoplasm 

 in which is imbedded the spiral band with its thousands 

 of cilia. Compared with the sperms of the pterido- 

 phytes, the sperms of the cycads aire immensely larger 

 and much less numerous. It must be a fact of some sig- 

 nificance that the living gymnosperms, with two or 

 three exceptions, have only two sperms, for the produc- 

 tion of sperms in pairs is universal from the liverworts 

 to the orchids. Whether the production of sperms in 

 pairs is associated with a separation of sexes is not 



