METABOLIC GRADIENTS IN AMOEBA 87 



terial, proteins, carbohydrates, and lipins, while the cavities of 

 the cells are filled with fluid. This structure is identical with the 

 alveolar and spumoid structure of Rhumbler and Butschli so that 

 any conclusions or theories which they have based on this struc- 

 ture must ipso facto be referred to the gel condition. 15 The endo- 

 plasm is a viscous sol, whose degree of fluidity is capable of con- 

 siderable variation. It is probable that the ectoplasm and the 

 endoplasm grade into each other imperceptibly. I am much in 

 favor of Clowes' interpretation, already referred to, that in pass- 

 ing from the surface of the protoplasm to the interior, a reversal of 

 phase occurs, the colloidal material forming the outer phase, or 

 disperse medium, in the surface layers, while in the interior it 

 forms the disperse phase and water containing a variety of ma- 

 terials in solution and suspension, is the disperse medium. 



It is Very probable that in amoeboid organisms the surface 

 layer will be found to show all possible gradations from real 

 fluidity to extreme solidity and rigidity. The Amoeba blattae 

 referred to by Rhumbler is undoubtedly one of the more fluid 

 forms, while Amoeba verrucosa has a highly rigid ectoplasm. 16 

 Different degrees of surface solidity appear to constitute the chief 

 differences between the two varieties of Amoeba proteus which 

 I have employed. The variety grown in hay culture has the 

 more rigid ectoplasm; its pseudopodia are more definitely local- 

 ized, are often very long and slender, do not tend to fuse, and 

 are very firmly fastened at their tips to the substratum. The 

 variety grown in wheat has broader illy-defined pseudopodia, 

 which are seldom long and slender but tend to fuse sidewise so as 

 to give a fan-like advancing end; the animal is not very firmly 

 fastened to the substratum, although more of its surface is in 

 contact with it. Owing to its greater rigidity, the hay variety 

 shows the disintegration gradient much more clearly than the 

 wheat variety. 



15 I wish again to point out that the evidence for this structure of emulsoid 

 gels is not as yet conclusive but if one assumes it to exist in protoplasm one must 

 realize the loss of fluid properties which its presence entails. 



" Amoeba terricola is said to be covered by a definite resistant membrane 

 (Grosse-Allermann, '09). 



