22 INTRODUCTION. 



That M. G. Thuret is in error in uniting all the species of 

 Vaiicheria into one, will, by a reference to the descriptions 

 and figures of the genus Vaucheria, which accompany this 

 work, be at once perceived. 



The animalcules contained in the cells of the filaments, 

 which occupy the interior of the globule of Chara, bear 

 considerable resemblance to the zoospores of the AlgcB ; 

 like them, owing their power of locomotion to the presence 

 of cilia, the anterior extremity of each being furnished with 

 two long lashes or cilia (see plate 62., Jig. 5, 6.). If the 

 views of physiologists, however, respecting them be cor- 

 rect, an essential and functional distinction exists between 

 them ; the one being the sporules themselves, and the other 

 the organism, or instruments, whereby those sporules are 

 fertilized. 



While the term zoospore has been applied to the moving 

 sporules of the Algce, the appellation of spore has been con- 

 ferred by some writers upon the large and usually elhptical 

 body formed in the different species of the genera Zygnema* , 

 Tgndaridea, Staiirocarpus, Mesocarpus, Mougeotia, Vesi- 

 culifera, and perhaps BulhoclicBte, by the union and con- 

 solidation of the contents of two cells either in the same or 

 different filaments. Concerning the nature of this body, 

 considerable difference of opinion has prevailed and still 

 obtains. Yaucher, who has so accurately described nu- 

 merous species of Conjiigatce, thus speaks of it: — "At last, 

 on the 25th Messidor, an IX, in examining the remains of 

 the Conferva jugalis MuUer, which I had followed since 

 the commencement of spring, I arrived fully and without 

 any doubt at this truth so desired, and which I had made 

 so long and so fruitlessly the object of my researches. 

 Almost at the same instant, and in the same day, or at least 

 in the same week, all the grains of the Conferva jugalis, of 

 which I had many thousands, opened themselves by one of 

 their extremities, in the same manner as the two cotyledons 

 of a seed whose embryo has become developed ; and from the 



* See the figures of those genera. 



