THE HIGHER CRYPTOGAMIA. 295 



forms two narrow closely approximated turns of a (usually) 

 left-handed spiral. These turns alone bear the cilia. 

 During the rapid motion of the spermatozoon in water its 

 wider, final turn, upon which the cilia are wanting, ap- 

 pears to be somewhat reduced in size (PL XXXVIII, fig. 

 28), but when the spermatozoon is killed with iodine, it ap- 

 pears on the contrary considerably enlarged (PI. XXXVIII, 

 figs. 30 33). This remarkable phenomenon depends upon 

 an organization hitherto (as far as is known) unique in 

 the vegetable kingdom. The end of the spermatozoon bears 

 on the inner side of its ultimate turn a wide fin-like 

 process, consisting of a delicate membrane, which during 

 the motion of the spermatozoon glistens like the undulating 

 membranes of the spermatozoa of toads and Tritons. 

 When the motion becomes more active the membranous 

 margin becomes invisible like the cilia ; it is only clearly 

 visible when the vital activity of the spermatozoon is on 

 the decline (PI. XXXVII, figs. 3033). The undula- 

 tions of the fin last longer than the oscillations of the 

 cilia. The hinder end of the spermatozoon appears still 

 somewhat pointed when the quiescent cilia of the fore-end 

 are already visible. The hinder end of the spermatozoon is 

 of a very delicate half- fluid consistence ; it attaches itself 

 easily to any object, and is then drawn out into long threads. 

 It often happens that a spermatozoon drags after it the 

 empty membrane of the mother-cell attached to one of 

 such threads, or that it fastens itself to a capillary root of a 

 prothallium (PI. XXXVIII, fig. 28 J ). Spermatozoa whose 

 motion, after many hours continuance, ends spontane- 

 ously, always exhibit a thin caudal appendage often of 

 very considerable length. The substance of their hinder 

 end has doubtless been drawn out into such threads, in 

 consequence of the spermatozoon having attached itself to 

 some body during its motion, and then torn itself away. 

 The substance of such spermatozoa exhibits, by the pre- 

 sence in it of vacuoles, manifest traces of a state of disten- 

 sion.* If the spermatozoa are killed with iodine they 



* In the ' Veigleich. Unters.,' p. 101, I treated the whip-shaped elongated 

 form of the hinder end as a peculiarity common to the spermatozoa of Equisctum, 

 an assumption which was grounded upon the frequent occurrence of such 

 peculiarity. 



