120 GENEEAL HISTORY OF THE INFUSOEIA. 



intensity of Kght may be too great, and destroy life ; and a great elevation of 

 temperature is less favom^able to vital activity than a moderate one. Cold 

 retards vital action, and if considerable, arrests it, except in the case of the 

 encysted beings, which are so modified by natiii'e as to resist its injmioiis 

 influence; these consequently persist through the winter when the motile 

 forms are cut off, and in the coming spiing bm\st forth into life. The same 

 provision which imparts to the encysted organisms a tolerance of cold, enables 

 them also to withstand the effects of evaporation, which to the unprotected 

 motile varieties is speedily destructive, unless, indeed, so gradual as to allow 

 them time to pass into the ' still ' form. 



Starch or cellulose may be detected chemically in the great majority of the 

 Phytozoa; and even where iodine fails to produce the characteiistic blue 

 colour during Hfe, it will at times act strongly when a breaking-up of the 

 contents follows evaporation or some other injmious influence. The efficiency 

 of nutrition is manifested by the decided changes, chemical and vital, which 

 are seen in constant operation within the beings — such as, among others, 

 the transformation of clilorophyll into starch, and of one or both these into 

 an oily matter. 



When in the ' stiU ' encysted condition (XIX. 4-1-69), aU nutritive changes 

 are at a standstill, and the organism may exist ^Aeeks, months, and even 

 years unchanged, until external conditions are sui3plied to awaken its latent 

 energies and to renew the cycle of Hfe. In this torpid form the spores are 

 carried about with the dust, or remain buried in the earth, or are elsewhere 

 hidden or stored up against the day of revival. 



The passage into the ' stiU ' condition by the throwing-out of an external 

 denser envelope and by the loss of ciHa, is governed, it would seem, in some 

 measure by external circumstances. Motile forms are replaced by the ^ stiU ' 

 in whole or in part, and with greater or less rapidity, by poimng the water 

 containing them into a larger and shallower vessel, and by gradual evaporation. 



The protoplasm of Phytozoa being homologous in all perceptible particulars 

 \\\th. the '■ sarcode ' of Protozoa, suffers, like it, the destructive process of 

 ' diffluence ' or ' deliquescence ' when evaporation reduces the quantity of 

 water around the improtected motile forms below the quantity necessary to 

 \'ital action. The first noticeable result of evaporation is, according to Cohn, 

 at least in the instance of Protococcus (op. cit. p. 538), a more rapid change 

 of figure and appearance, followed, if the evaporation continue, by diffluence, 

 in which he distinguishes two stages or phases : — '' In the fu'st, the outlines 

 appear less sharply defined, because the coloured substance is somewhat 

 retracted from the border of the piimordial cell ; the cells become flattened, 

 and at the same time ^^ider : the contents are also now altered ; previously 

 more homogeneous and transparent, they now become thi^oughout granular, 

 and the red substance runs together in large drops. At this time the forma- 

 tion of vacuoles commences ; and their number continues to increase. In this 

 way the interior of the primordial cell again becomes colourless, clear as 

 water, and the granular coloui-ed contents pressed against the walls. . . .The 

 figiu-e of the cell in the warm time is so much expanded, that it comes to be 

 apphed upon the wall of the enveloping cell, alternately filhng it altogether, 

 so that the entire zoospore appears to consist of only a single coloiu'cd gra- 

 nular vesicular disc, corresponding in size with the original enveloping cell." 



Multiplication and Reproduction of Phytozoa. Fission : Macrogonidia ; 

 MicROGONiDiA : Encysting process : Phases of existence. — The multiplica- 

 tion of the individuals of the species of Phytozoa is provided for by the 

 process of self- division, deduplication, or fission. This takes place according 

 to the plan obtaining in vegetable and animal cells in general. 



