266 PROTOPLASM 



exception can be taken to it. On the contrary, I Lave 

 described above a number of facts with regard to Gromia 

 Dujardini from which it follows quite necessarily that 

 homogeneous protoplasm also possesses an alveolar structure, 

 for otherwise it would not be explicable how it could arise 

 so suddenly from alveolar protoplasm, or how, on the other 

 hand, it could be again converted into the latter. 



In this phenomenon it remains for the present still unex- 

 plained why the granular contents of the interior do not 

 penetrate into the homogeneous protoplasm. There is no 

 intrinsic reason why this should be so. Schwarz (1887) 

 has observed that granules which are suspended in a viscid 

 fluid usually keep at a certain distance from the surface, 

 and hence he thinks that the hyaline non-granular marginal 

 protoplasm, such as is often seen in vegetable cells also 

 (the so-called " Hautschicht " of the botanists), may be 

 referred to this physical phenomenon. Apart from the fact 

 that I never observed the phenomenon described by Schwarz 

 in my numerous experiments on oil-drops with which finely- 

 divided lamp-black had been mixed, I cannot accept this 

 explanation for the further reason that in Amcebse one 

 frequently notices that when the marginal border is wanting 

 the granules penetrate as far as the surface, or at least as 

 far as the alveolar layer, which could not well take place if 

 the explanation given by Schwarz was correct. On the 

 other hand, however, from the fact that non-granular homo- 

 geneous protoplasm as soon as it passes into the alveolar 

 condition becomes distinctly granular (that is to say, that 

 the nodal points of the alveolar framework which have now 

 become visible, impart this character to it), the view already 

 stated may be proved with certainty, namely, that the granular 

 appearance of the protoplasm depends to a great extent on 

 the alveolar structure, since both the nodal points and the 

 optical properties which have already been pointed out in 

 the case of artificial foams cause the same appearance 

 in them. 



