156 T. a. o'donohoe on the minute 



layer upon the one nearest the eye, just as a picture is thrown 

 from the optical lantern upon a canvas screen. The fibrils or 

 grating is the real structure, of which the texture is concealed, 

 even as that of the canvas screen is concealed by the picture." 

 So much for this new theory. We can consider only a few of 

 its points. The figures given on page 289 are, we are told, 

 photomicrographs of the two separated membranes of a valve of 

 Pleurosigma angulatum. If two really good photographs were 

 taken of these two membranes at about 4,000 diameters, they 

 would, in my opinion, make an end of Mr. Smith's theory, but 

 instead of giving his readers two such images, which would be 

 extremely interesting and valuable, he gives them a great 

 number of outers ides and innersides which, he tells us, do not 

 show the structure at all, and are therefore of very little value. 

 Indeed, I may say for myself that I attach little or no value to 

 interpretations of fine diatomic structure other than those of 

 thoroughly separated single membranes. Of these only can we 

 speak with a fair degree of certainty. 



Turning now to page 331, we find that Mr. Smith says : " Fig. 

 14 is from an innerside of another valve (of P. formosum), the 

 first ever seen and taken, showing the fracture through un- 

 doubted perforations," and Mr. Nelson, being called to his aid, 

 testifies that " Mr. Smith has found this fracture, had shown it 

 to him, and that at any rate the fracture did run through the 

 holes." So, too, Mr. Smith cites the testimony of Dr. Dallinger, 

 who says : " In Plate I. fig. 1 (Carpenter on the Microscope) we 

 have a photograph of his showing the inside of a valve of 

 Pleurosigma angulatum magnified 1,750 diameters, exhibiting 

 the " postage-stamp fracture." The postage-stamp fracture is, 

 as everybody knows, a fracture through the holes, so that we 

 have these two great authorities testifying to the fact that these 

 photographs of Mr. Smith show fractures through holes, or, as 

 Mr. Smith calls them, undoubted perforations. His theory being 

 that there are neither holes nor beads in the valve of a 

 Pleurosigma, does he now repudiate these photographs and 

 these testimonies'? He speaks of his fibrils forming interspaces, 

 chains and gratings, and it would be interesting to have his 

 definitions of these terms. Can there be chains or gratings 

 without intervening spaces, i.e. holes or perforations ? 



Fig. 18, page 333, " The innerside of Pleurosigma angulatum 



X 3,770," by no means a sharp image, shows, nevertheless, holes 



galore to any one who is not blind or unwilling to see them. 



