PLASMATIC MEMBRANES 25 



hence capable of exerting a definite influence continuously at the 

 same point. 



The attribution of this controlling influence to the ectoplast must 

 of course by no means be held to imply that the latter has a monopoly 

 of morphogenetic activity. It is on the contrary highly probable, as 

 will lie shown later on, that the formative processes of the cell in 

 general, and particularly those which relate to the cell-wall,. take place 

 under the directive influence of a totally different cell-organ, namely, 

 the nucleus, and that the latter as it were employs the ectoplast as an 

 executive agent. On account of its superficial position the external 

 plasmatic membrane is that part of the protoplast which is first affected 

 by external stimuli, and it is accordingly not improbable that the 

 ectoplast represents the general perceptive organ of the cell ; this 

 supposed special function of the ectoplast cannot, however, be considered 

 in detail until a later occasion (cf. Chap. XII.). 



It is maintained by de Yries that both the external and the 

 internal or vacuolar plasmatic membranes are independent, autonomous 

 protoplasmic organs, invariably derived from pre existing structures of 

 the same kind, and never arising de novo by differentiation from 

 ordinary polioplasm. This assumption is based upon the following 

 observations, among others. If the ectoplast is subjected to mechanical 

 injury as, for instance, when a filament of Vauch&ria is cut across 

 its severed margins always fuse together again immediately: further 

 the vacuolar membrane can be artificially isolated from the surrounding 

 polioplasm without at once losing its vitality or the organisation 

 associated therewith. De Vries also cites certain observations made 

 by Went, according to which vacuoles are distributed throughout every 

 protoplast and multiply by division only, while those which appear to 

 be in the nascent condition are in reality developing from pre-existing 

 vacuole-forming organs or tonoplasts. (Went and de Yries apply this 

 term also to the adult vacuolar membranes.) 



This view is opposed by Pfeffer, who holds that the ectoplast and 

 the vacuolar membranes are not autonomous protoplasmic organs com- 

 parable to nuclei or chroinatophores, but that on the contrary both 

 may be produced anew, as required, by differentiation out of ordinary 

 cytoplasm ; the latter, in fact, possesses an inherent capacity of 

 separating itself, when necessary, by the formation of a special limit- 

 ing layer, both from the surrounding medium and from included sap- 

 cavities. Apart from theoretical considerations, Pfeffer bases his 

 opinion principally upon the fact that formation of vacuoles in no 

 respect different from normal vacuoles may be artificially effected by 

 introducing minute crystals of asparagine or calcium sulphate into the 

 interior of a Myxomycete-plasmodium. This is not the place to deal 



