Protomyxa. 6 1 



easily into the surrounding medium ; but during the 

 resting stage, manifestly, the rapid escape of effete matter 

 would not be possible. Hence the excreta would become 

 more or less aggregated round the organism itself. The 

 organism becomes, in other words, encrusted or enclosed by 

 its own excreta. The fact that the cyst is at first wanting, 

 ,then thin, and gradually becomes thicker, is thus explained. 

 Further, when we examine into the chemical nature of the 

 cyst we find it to be composed of a substance exceedingly 

 common in the plant world, namely cellulose. Now, one of 

 the most apparent physiological distinctions between animals 

 and plants is, that while the power of motion is characteristic 

 of the former it is not so of the latter. Hence we are not 

 astonished to find that cellulose, which we have seen to be 

 in some way associated with rest, is a substance of rare 

 occurrence in the animal world ; and that in those animals 

 in which it, or some substance chemically allied, does occur 

 the power of movement has been nearly or entirely lost. 



Chemically, cellulose (which must be the subject of more 

 careful consideration subsequently) is composed of carbon, 

 hydrogen, and oxygen (the two latter in the proportion in 

 which they occur in water). We have here the elements of 

 carbonic acid and water, while the oxygen which the car- 

 bon has lost is probably used up in various concomitant 

 chemical changes taking place in the encysted organism. 



The first result of this temporary cessation of activity, 

 represented by the encysted stage, is the formation of a 

 store of energy (potential), which first manifests itself 

 kinetically, under special circumstances, in the subdivision 

 or segmentation of the protoplasm into masses, which by- 

 and-by escape upon the rupture of the cyst (probably by 

 internal pressure). The organisms which escape are actively 

 motile masses of protoplasm, each provided with a flagellum 

 by means of which motion is effected. Hence this may be 

 known as the flagellate stage. As in the amoeboid condi- 

 tion, it is possible, by the application of a gentle heat, to 



