THE SARCODINA 



157 



explanations that have been given fail to account for certain com- 

 plexities in behavior which are disclosed by more thorough study. 

 For example, it was at one time supposed that the movements of an 

 amoeba were caused by the same physical phenomena as the 

 changes visible in a drop of clove oil when placed on a slide in a 

 mixture of 3 parts glycerine and one part 96 per cent alcohol. 

 Such a drop will change its form, send out " pseudopodia," and 

 move about much as does an amoeba. Or, a mass of glycerine, 



8 



S 



Fig. 86. — Locomotion in amoeba as recently described by Mast. 



AccordinR to this account, the amoeba consists of an inner granule-containing fluid 

 substance, the plasmasol, surrounded by a more solid layer of similar composition, the 

 plasmagel, which are together equivalent to what is ordinarily termed the endosarc. Out- 

 side there is a hyaline portion of the plasmagel, which is almost homogeneous optically, 

 and an outermost layer, the plasmalemma. These last together constitute the ectosarc. 

 During locomotion the plasmasol and plasmagel become transformed into one another 

 after the manner shown in the figure. The plasmasol moves forward and at the end of 

 the advancing pseudopod becomes transformed into the layer of plasmagel, which in turn 

 is becoming plasmasol at the posterior end, "much as a chimney might be extended by 

 carrying brick and mortar up through it and depositing them on the wall surrounding the 

 opening." 



(7, region of gelation of plasmasol resulting in forward extension of the granular layer 

 of the plasmagel; (/', region of gelation resulting in formation of hyaline layer of plasmagel; 

 It, nucleus; pg, plasmagel; pi, plasmalemma; ps, plasmasol; s, region of solation resulting 

 in transformation of plasmagel into plasmasol. (Reproduced from the original drawing by 

 courtesy of S. O. Mast.) 



placed in a watchglass of rather thick lubricating oil, can be made 

 to roll about in a suggestive manner. If soot particles are added 

 to the glycerine they are held in suspension much as are the bodies 

 in the endoplasm of an amoeba, and the movements have an even 

 greater resemblance. These simple imitations now appear to offer 

 inadequate explanations of amoeboid movement, although it may 

 be that the phenomenon is capable of physico-chemical explana- 

 tion in more complex terms. 



