THEORIES CONCERNING RA DIA TE A PPEA RA NCES 2 5 7 



in the descriptions of these structures, namely, how we are 

 to regard the aggregate condition of the substance of the 

 alveolar framework in their case. If they exist per- 

 manently, it seems quite certain at the outset that their 

 alveolar framework must be rigid, or at least so viscid that 

 it only alters its configuration, in obedience to the laws of 

 fluid foams, with extreme slowness. In any case it seems 

 beyond a doubt that structures of this kind cannot 

 exist permanently if we have to deal with fluid substances 

 forming the framework and the contents of an alveolar 

 meshwork, which is itself free in a surrounding fluid. The 

 matter, however, is not simple here, but the form of all these 

 protoplasmic bodies proves at once that they must be 

 surrounded by a firm membrane. Moreover, these cells are 

 so connected in the interior of the organism with others, or 

 even with undoubtedly solid parts, that their form will 

 become fixed accordingly. Now how a viscid foam, which is 

 enclosed in a firm elastic envelope, will behave during ten- 

 sion of this membrane, does not seem to me quite easily 

 decided a priori; in fact, so far as the laws of foam forma- 

 tion have been investigated, it seems to me even possible 

 that it would be converted into a foam with elongated 

 meshes, and would persist as such if the meshes were not 

 too much stretched. 



In opposition, therefore, to my former assumption (1891) 

 I think we must admit it to be possible that these per- 

 manently fibrous alveolar structures of the axis cylinder, 

 etc., may be of a viscid nature. 



(/) Theories concerning the Causes of Radiate Appearances 



Very various views have in the course of time been set up 

 with regard to radiating protoplasmic structures, the prob- 

 able cause of which we have above sought to refer to processes 

 of diffusion. I think there is no need to enter into a detailed 

 discussion of all the opinions, but I will confine myself to the 

 description of the principal points of view that have been taken 

 up with regard to this matter. At first of course the ideu wa^ 

 put forward that the radiate appearances in cell division must be 

 due to a kind of attraction which was exerted by the poles of 

 the nuclear spindle upon the particles of protoplasm, or more 



