261 THE MICROSCOPE. 



with the smaller motile spores observed by Thuret and 

 A, Braun in other Algae (the Fucoid, &c.), associated with 

 the larger germinating spores, themselves deprived of the 

 germinative faculty. 



It appears that both longitudinal and transverse division 

 of the primordial cell may take place ; but that the 

 vibratile cilia of the parent cell retain almost to the last 

 moment their function and their motion after the primor- 

 dial cell inclosed by it has long been detached as a whole, 

 and become transformed into the independent 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 dis- 

 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 be 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 divisional generation will have 

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

 will be found covered with a new generation of self- 

 dividing colls, 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 the propagation is 

 very remarkable. It is only necessary to pour water 

 from a smaller into a larger and shallower vessel, or one^of 

 a different kind, to at once induce the commencement of 

 segmentation 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 conducive 



