240 PROTOPLASM 



this cell plate the membranes of the cell. Yet he draws no 

 distinct alveolar layer on the free surface of the segmentation 

 cells, although it is certainly present here in like manner. That 

 it is more plainly noticeable in the parts of the cells which 

 border upon one another seems natural, since it possesses in this 

 situation double the thickness, and is therefore more striking. 

 Of course it is no concern of mine to try to clear up the matter 

 without new investigations of my own upon the objects in ques- 

 tion. I hope, therefore, that these conjectures will not be 

 misunderstood. 



(e) Cell Membrane, Cuticulce 



Since we have just seen that Carnoy without doubt deals 

 with our marginal alveolar layer universally as a cell 

 membrane, and Frommann also later (1890) refers the 

 alveolar layer of the Infusoria to the cell membranes with- 

 out one word in justification of this course, I must say a 

 few words on this point. 



The reasons for which the alveolar layer of the Infusoria 

 cannot be placed among cell membranes in the usual sense 

 have been set forth at length by me before (1887, p. 1268). 

 The chief reason is that this layer is just as easily destroyed 

 or rendered fluid by pressure, as the rest of the proto- 

 plasm from which it shows no essential difference with 

 regard to tingibility and chemical properties, as far as this 

 has been investigated. Besides this its behaviour in 

 division must be taken into account, when it follows the 

 body like an external layer of protoplasm, and during the 

 fusion of Infusoria in conjugation. All this proves that the 

 alveolar layer of Infusoria cannot be directly compared with 

 an isolated, resistant membrane, of the kind which we are 

 familiar with in typical cell membranes. Their general 

 properties show that they must consist of a substance 

 agreeing essentially with the rest of the protoplasm, which 

 can have only undergone slight chemical modifications in 

 them. On the other hand, we can trace the alveolar layer 

 even down as far as amoeboid protoplasmic bodies, in which 

 there can no longer be any question of a cell membrane. 

 Although, therefore, I am not inclined to allow that a mar- 



