THE LIVING SUBSTANCE. 15 



Some compound inclusions have become very familiar to us 

 under the names of starch, yolk, pigment, the " granules " of 

 the network ; and chromatin, as fibres, granules, masses, or 

 networks. 



Yet even of these long-known substances much remains to 

 be learned. Many questions that now leap into almost impera- 

 tive urgency have, up to this time, scarcely shaped themselves. 



Which of these substances are stimuli ; which are food for 

 the final protoplasm ; which are excretions, which secretions ; 

 which are means to an end ; which attained ends } In other 

 words, which are final, which intermediate, agents in producing 

 the physiological results we can trace .■' 



Such questions are puzzling enough when applied to the ele- 

 ments of the structure of Biitschli. More puzzling still must 

 it be to answer which of our results, in any given area, are due 

 to the inclusions of this alone ; which to the interalveolar sub- 

 stance, with its inclusions. And finally, may not some of the 

 results had in the inclusions of the structure of Biitschli, be 

 due to secretions or excretions of the interalveolar substance 

 under irritation } 



The substance called j/ oik seems to me one of the most inter- 

 esting problems. When one considers that in cases such as 

 are met with in certain rotifers, the whole of a huge ovary, con- 

 taining material for a score of eggs, is converted, under certain 

 conditions, into a single egg ; and that nuclei, as well as the 

 already prepared yolk, go to form the "yolk" for this monster 

 egg: the question naturally arises; which part of the whole mass 

 of intermingled material goes to make up the organism which 

 issues forth in the following spring .'' 



We know that yolk disappears largely, if not wholly, during 

 process of development of the immature creature. But let me 

 emphasize here what all the facts collected are ceaselessly 

 emphasizing: that optical disappearance, under such conditions 

 as exist in the protoplasmic froth, may mean several widely 

 distinct sets of phenomena. 



Given the finer structure of the interalveolar substance, 

 many obscure phenomena associated with the life history of all 

 these substances become more intelligible. 



