THE MARGINAL ALVEOLAR LAYER 237 



question in favour of the alveolar theory. I have before 

 shown that especial relations exist at the surface of the 

 protoplasm, since the alveoli of the outermost layer are 

 always directed vertically to the surface, in consequence of 

 which the thin radially striated layer, termed the marginal^ 

 alveolar layer, comes to be formed. I have demonstrated this 

 marginal alveolar layer in quite a number of cells, etc., and 

 may further add that Schewiakoff and myself have further 

 proved its existence both in smooth and transversely striped 

 muscle cells (1890, 1891). 



It has, however, further been shown that this alveolar 

 layer is in no way a special kind of membrane at the 

 surface of the cells, for it occurs in the same manner alscr 

 round the drops of protoplasm that are formed by crushing 

 either Miliolids or Gromia Dujardini. 



On the other hand, we also found that a marginal layer 

 of alveoli is always marked out at the surface of artificial 

 drops of foam, and we were easily able to explain to our- 

 selves how and why it must always make its appearance 

 there. This agreement between the oil-lathers and proto- 

 plasm I regard as a proof that an agreement also exists in 

 their remaining structure. At any rate I am not aware in 

 what way the theory of a supporting framework would give 

 an explanation for the appearance of the alveolar layer ; 

 in any case it would need for this purpose, like every theory 

 built up on a false foundation, certain subordinate hypotheses, 

 by which means it would prove itself afresh to be im- 

 probable. 



Since the marginal alveolar layer must be, according to our 

 conception of the structure and physical nature of protoplasm, 

 of quite universal occurrence, we must inquire for ourselves 

 whether there are -any statements in the earlier literature which 

 justify the supposition. Kupffer as far back as 1870 figured - 

 the outermost meshes in the follicle cells of the Ascidian ovum 

 as distinctly directed vertically to the surface. Since, however, 

 as was pointed out above (p. 162), it is rather uncertain whether 

 the alveolar structure of these cells is not a coarse vacuolisation, 

 it remains rather doubtful whether we have here a real alveolar 

 layer. Just as little can it be definitely determined whether 

 the radially striated wall which he described in 1874 in the so- 



