2 BIOLOGICAL LECTURES. 



we are not yet in a position to justify any very certain or far- 

 reaching conclusions. 



I would like, at the outset, to express the opinion that, if we 

 except certain highly specialized structures, the hope of find- 

 ing in visible protoplasmic structure any approach to an un- 

 derstanding of its physiological activity is growing more, instead 

 of less, remote, and is giving way to a conviction that the way 

 of progress lies rather in an appeal to the ultra-microscopical 

 protoplasmic organization and to the chemical processes through 

 which this is expressed. Nevertheless, it is of very great im- 

 portance to arrive at definite conclusions regarding the visible 

 morphology of protoplasm, not only because of its intimate 

 connection with all the problems of cell-morphology, but also 

 in order to find the right framework, as it were, for our physio- 

 logical conceptions, and thus to gain suggestion for further 

 physiological and chemical inquiry. And this must be my 

 excuse for reviewing a subject which is still so largely obscured 

 by doubt, and of which the outcome gives, after all, so little 

 satisfaction. 



It is especially important in this field of biological inquiry 

 to distinguish clearly between theory and observed fact ; for 

 theories of protoplasmic structure have always far outrun the 

 actual achievements of observation. From the time of Briicke 

 (one of the first to insist that protoplasm must possess a far 

 more complicated organization than that visible under the 

 microscope), speculation has gone steadily forward, to reach, per- 

 haps, its most elaborate expression in Weismann's interesting, 

 but unconvincing, work on the germ-plasm — an elaborate specu- 

 lative system built out of hypotheses which for the most part 

 float in the air without visible means of support. We need not 

 consider this side of the subject in extcnso, but I will ask atten- 

 tion, for a moment, to what is the most characteristic and, to the 

 morphologist, the most interesting point in these speculations, 

 namely, the doctrine of genetic continuity as applied to the 

 corpuscular, or micellar, theory of protoplasm. We are all 

 familiar with the successive steps by which that doctrine gradu- 

 ally developed. Harvey's celebrated formula, ex ovo omnia, — 

 or, as usually quoted, omne vivum ex ovo, — took with Redi the 



