24 ANDREWS. 



[20] In one respect the kinship between protoplasm and arti- 

 ficial foams, as established by Butschli's masterly researches, 

 holds good and is not to be shaken. As to the formation of 

 pellicles, the physical nature of the substance seems to rule, and 

 never, so far as I have seen, is it set aside by those controls which 

 elsewhere appear to dominate from time to time that physical 

 mastership of the elements Butschli has demonstrated. 



This fact, as pointed out above, is one of the strongest evi- 

 dences of the true nature of the substance. 



From mass pellicles in all their varieties,^ through the series 

 of inclusion pellicles down to alveolar lamellae and pellicles of 

 the finer foam inclusions; the living substance maintains its 

 habit of surrounding all physical differences of contact with a 

 continuous film of its own material. 



But this basic unity of structural form covers an infinity of 

 structural differences, of which many organisms; not less those 

 which for many years biologists have termed "simple," than 

 members of the highest groups; will furnish abundant proof. 



Only the most obvious of these have so far been noted : 

 vast fields for research are now seen to open out in respect to 

 those which are not only less conspicuous but also in many 

 instances more evanescent organizations of the elements. 



In an amoeba, for instance, the peripheral pellicle which 

 stands for cell wall, the ectosarc possibly, the contractile vac- 

 uole, the food sacs, the nucleus; — these have been taken to 

 be the limit of organization of the substance in this lump of 

 "primitive protoplasm." 



So far as these well-known areas of differentiation of the 

 living substance go, they were seen, with respect to the foam 

 structure, to be optically separated from each other by charac- 

 ter of their inclusions and of the continuous element ; and by 

 the mode of distribution of these two in relation to each other, 

 not only as permanent differences but as differences from 

 moment to moment. 



Besides the broad areal differences noted, there exist local 

 differentiations more or less unstable, to the point of such 

 evanescence often as makes it difficult to catch a glimpse of 



^ See also Ectosarc. 



