264 THE MICROSCOPE. 



correspond with the smaller motile spores observed by 

 Thuret and A. Braun in other Algae (the Fucoid, &c.), 

 associated with the larger germinating spores, them- 

 selves deprived of the germinative faculty. 



It appears that both longitudinal and transverse 

 division of the primordial cell may take place ; but that 

 the vibratile filaments of the parent cell retain almost to 

 the last moment their function and their motion after 

 the primordial cell inclosed by it has long been detached 

 as a whole, and become transformed into the indepen- 

 dent secondary cells (fig. 144, G). 



The most striking of the vital phenomena presented by 

 this organism is that of periodicity. Certain forms for 

 instance, encysted zoospores, of a certain colour, appear in 

 a given infusion, at first exclusively, then they gradually 

 diminish, become more and more rare, and finally dia- 

 appear altogether. After some time their number again 

 increases, and reaches as before to an incredible extent ; 

 and this proceeding may be repeated several times. 

 Thus, a glass which at one time presented only still 

 forms, contained at another nothing but motile ones. The 

 same thing may be observed with respect to segmen- 

 tation. If a number of motile cells be transferred 

 from a larger glass into a small vessel, it will bo found, 

 after the lapse of a few hours, that most of them have 

 subsided to the bottom, and in the course of the day they 

 will all be observed to be on the point of subdivision. On 

 the following morning the provisional generation will 

 have become free ; on the next, the bottom of the vessel 

 will be found covered with a new generation of self-divid- 

 ing cells, which again proceed to the formation of a new 

 generation, and so on. This regularity, however, is not 

 always observed. The influence of every change in the 

 external conditions of life upon propagation is very re- 

 markable. It is only necessary to pour water from a 

 smaller into a larger and shallower vessel, or one of a dif- 

 ferent kind, to at once induce the commencement of seg- 

 mentation in numerous cells. The same thing occurs in 

 other Algae ; thus the Vaucheria almost always develop 

 zoospores, at whatever time of year they may be brought 

 from their natural habitat into a room. Light is con.- 



