144 



ANDREWS. 



assumed to be selective organs for the substance, that is nutri- 

 ment control areas. Whether these areas are this only or 

 whether they serve also as substance ganglia, carry the form 

 and function memory of the substance as such and stand for 

 the nervous centre or brain of the cell area, must rest for 

 future research, but the facts which connect them both with 

 the cytoplasmic granules and with nervous structures have been 

 pointed out earlier in the article. 



Parasitism. 



[143] I have said that many areas which as substance 

 organs function markedly for organized contractility or irrita- 

 bility, are formed of more or less unstably segregated proto- 

 plasm in which the alveolar inclusions of the actively functioning 

 substance are uniformly fluid. These inclusion fluids are 

 carried from assimilating portions of the general substance, or 

 received by dialysis, or even from wandering interalveolar 

 foam. Such areas depend upon assimilative areas for their 

 special environment. To this extent they are parasitic. 

 Whether they in their turn serve assimilative areas directly 

 with their products, or indirectly by their activities, is aside 

 from the immediate issue. Much interalveolar substance of 

 Biitschli's structure forms a constant typical area of this sort. 

 Parasitism is used here, in that broader, more genial, sense 

 which does not preclude the idea of mutual benefits between 

 dependent and supporting areas. In such organisms as 

 amoeba where function and structure seem alike interchange- 

 able, the substance forming true ectosarc may but a short time 

 before have taken part in active assimilation areas, and even 

 where ectosarc is a quite stable formation, its interalveolar 

 foam may pass as an active carrier to and from these. By 

 watching for hours the progress of assimilation in Protozoa, I 

 have many times seen that there is at intervals a determination 

 of fluid in considerable amounts to the food sacs — the tempo- 

 rary stomachs ; and again a sudden redistribution at intervals, 

 or a more or less steady draining, of fluids from such sacs into 

 the surrounding protoplasm. These phenomena are mingled 



