1916] Wilsou: On the Life-Histonj of a Soil Amoeba 261 



final absorption, suggest the restoration of this balance; and the 

 failure of inducements for the amoeba to come out suggest that it is a 

 depression period, and one of internal readjustment, since, when the 

 ehromidia disappear, the amoeba comes out and goes through another 

 vegetative cycle. 



It is the mere elimination of nuclear substance and is not sufficient, 

 as Hartmann (1913) says, to be interpreted as chromatin reduction in 

 gametogenesis. If it were, there would be fertilization after the 

 amoebas came out of the cysts, not a single case of which has ])een 

 found, though preparations have been fixed at short intervals during 

 excystment extending over a period of more than twelve hours. 



The difl'erences in striicture and fate of the ehromidia of tropho- 

 zoite's and those of cysts, though chemically alike in so far at least as 

 their reaction to stains is concerned, suggest that they are different 

 in kind, the former being generative chromatin and the latter vegetative 

 chromatin. However, the proof is not conclusive. All ehromidia of 

 the trophozoite may not produce new nuclei. Those that do may be cut 

 off b^' mere chance and then may or may not reorganize into nuclei of 

 new individuals. The ehromidia of cysts may not always be absorbed. 

 However, they sometimes behave as described above and as far as the 

 evidence goes, they are of the two kinds. 



IT. THE CYST 



1. Characters 



The cysts are .spheroidal, 7-14/1. in diameter, and have transparent 

 hyaline walls with definite "marlvs" or openings which are variable 

 in number (pi. 23, fig. 114). The amoeba within a mature cyst is free 

 from food and contractile vacuoles. It is so translucent that it may 

 be studied without difficulty in both living and stained material. The 

 nucleus with its large karyosome is clearly discerned. 



The mature cyst is double-walled. Two walls may not always be 

 distingui.shed in that stage, but they are clearly defined in its develop- 

 ment, in which there is first formed a very thin" outer wall in which 

 no openings have been observed (pi. 21, fig. 79). Within this is later 

 formed a thick wall in which from three to eight openings have been 

 found, each in a local thickening. 



In a newly formed cy.st the cytoplasm ma.v fill the entires pace 

 within the cyst wall, but later withdraw more or less from the wall 

 (pi. 21, fig. 81), apparently by condensation. It is dense and slightly 



