THE LIVING SUBSTANCE. 03 



Conversely, wherever there were seen such refractive portions 

 of hnes of continuous substance, I either found directly by 

 change to higher powers, or, where the limit of magnification 

 had been already reached, was able to argue from other activi- 

 ties of the same area, or from associated optical phenomena, a 

 true foam structure. 



It frequently happens that there is an alveolar arrangement 

 linear in two directions, and that parallel lines of an optical 

 reticulum cross each other at sharply defined right angles, or 

 at equal angles of other sorts, yet in these cases there may be 

 true and very marked strial emphasis upon one set only of these 

 lines ; or may be upon both in alternation ; or equally upon 

 both, being in this last case markedly different from surround- 

 ing optical network lines also caused by linearly placed alveoli. 



In both Protozoan and Metazoan groups, striations associated 

 with contractile activities appear singly, and in simple or com- 

 pound groups. Even so comparatively simple a form as Vorti- 

 cella has a footstalk in which I find no less than five different 

 areas of organized foam structure grouped in physiological 

 alliance, each bearing some special part in the contractile ac- 

 tivity ; and there are indications of even more such differentia- 

 tions beyond our reach. 



It is often impossible to resolve with striations, cross lines 

 of an alveolar network, simply because the striae have been 

 made visible by increase of mass of the interalveolar substance, 

 — with increase also perhaps of its refractive power along those 

 lines, — in a vesicular structure whose lamellar substance, with- 

 out such increment, were far beyond our reach. Sometimes 

 also, striations coincide, not with an optical reticulum of the 

 plane in observation, but with that of a plane at right angles to 

 this. Such a case was found in the cuticle of Stent or ccernletis. 



If strial or fibrillar appearances of contractile areas, as cor- 

 related with physiological function of the substance there, are 

 grasped in relation to Biitschli's structure, it becomes pos- 

 sible to understand how these results apply to phenomena 

 found in the finer structure. 



As a typical instance of contraction organized on a basis of 

 Biitschli's alveolar structure, I will take the cuticle of Epistylis 



