296 I10FME1STER, ON 



usually unrol themselves like a snail (PI. XXXVII, figs. 

 31 — 33) ; it is but rarely that the individual turns remain 

 at a distance from one another, as is the case during the 

 motion. The motile cilia appear stiff and extended when 

 the spermatozoon is quiescent ; their direction is not radial 

 to the axis of the spiral of the spermatozoon, but is turned 

 backwards. 



The mode in which portions of the spermatozoon remain 

 attached to the mother-vesicle is very various. Very fre- 

 quently the thick fore-end remains inside the spherical 

 vesicle, the lower turns protruding out of the fissure, and 

 causing by the oscillation of their cilia a restless reeling 

 motion of the organ and its mother-cell. More rarely the 

 fore-end is free and the hinder-end enclosed in the vesicle. 

 In such cases the motion is more regular and more rapid. 

 It more often happens that the cilia of the thickest end of 

 the spermatozoon protrude out of a fissure in the vesicle. 

 The continual rolling motion of such spermatozoa very much 

 resembles that of many infusoria. 



I have seen the motion of the spermatozoa of Equisetum 

 arvense last for five hours. The sensitiveness of the sper- 

 matozoa to external influences appeared to me much less 

 than that of ferns. Water containing much gypsum, which 

 acted in a decidedly injurious maimer upon the spermatozoa 

 of Asplenium septentrionale, had not the slightest effect upon 

 those of Eq. arvense, pahcstre, and limosum. 



In JEq. limosum I found the first ripe antheridia five 

 weeks after the sowing of the spores (on the 1st of July), 

 in JEq. arvense thirteen weeks after (at the end of July) ; 

 in one case four weeks only after the sowing (at the end of 

 May). The number of the antheridia upon one prothallium 

 is sometimes as many as sixteen in Eq. arvense. The inner 

 wall of the cavity of antheridia which have discharged 

 their contents assumes a deep brown colour. The escape 

 of the cells enclosing the spermatozoa certainly takes place 

 spontaneously ; heaps of agglomerated dried mother-cells 

 of spermatozoa are often found at the apex of empty anthe- 

 ridia. 



Numerous obstacles seem to interfere with the natural ger- 

 mination of the Equisetacese. Although I have often searched 



