552 E. A. MINOHIN. 



problem why the sclerite should have the monaxon form, still 

 less of the triradiate and quadriradiate type. 



Dreyer's theory assumes the well-known theory of Biitschli 

 (1892) as to the ultimate structure of protoplasm. Let me 

 begin, therefore, by declaring myself also a firm believer in 

 Biitschli's views ; the translation published by me of his great 

 work may perhaps be taken as a sufficient guarantee of my 

 acquaintance with his theories. Biitschli regards protoplasm 

 as having the structure of a very fine emulsion or foam ; 

 droplets of a watery fluid or enchylema are suspended in a 

 denser and more viscid fluid which constitutes the alveolar 

 framework. The relations of these two parts are similar as 

 regards structure to those of an ordinary froth or lather, the 

 enchylema corresponding to the air, the alveolar framework to 

 the liquid, whatever it may be, of which the froth is composed. 

 In cross-section the alveolar framework would appear as a fine 

 network containing meshes of various sizes which were filled 

 originally with the enchylema. In addition to these two parts, 

 all known protoplasm shows a great number of granules or 

 microsomes, varying greatly in size, consistency, appearance, 

 and chemical reactions, but always contained in the alveolar 

 framework and lodged at the nodes of the reticulum. Proto- 

 plasm, therefore, consists of three constituent parts, — alveolar 

 framework, granules, and enchylema. The vacuoles, on the 

 other hand, which are so often a conspicuous feature of proto- 

 plasm, and which may contain various bodies, are not to be 

 regarded as another primary element, but as produced by the 

 fusion or running together of alveoli, just as in a froth a large 

 bubble may arise by the breaking down of smaller ones. 



Dreyer assumes that the sclerites are first deposited at the 

 nodes of the alveolar framework, and that the supposed primi- 

 tive tetraxon type of all spicules is the mechanical result of 

 this fact. In the first place it may be pointed out that this 

 assumption remains to be proved, for Calcarea at any rate. It 

 is by no means impossible that the spicule at its first appear- 

 ance is deposited in something corresponding to a vacuole, and 

 if so, Dreyer^s explanation would no longer apply. We may 



