September, 1912. 



KNOWLEDGE. 



remainder. Both pictures are taken from the same 

 spot with only just a shght change of focus. Where 

 marked with a X they show in what manner the 

 minute hexagons are formed, one focus presenting 

 them black and the other white. 



If the reader will now refer to the article of last 

 year he will tind in Figure 18, from the inner 

 side of the valve of P. iin<>iilafiiin, a single detached 



matter of fact they have none.) An irregular-shaped 

 structureless membrane is stretched over the top of 

 them, hiding the contours altogether. Where the 

 ends of the fibrils have been broken off is indicated 

 by the stumps left, and between them are caught 

 little points of light, showing how the focal images 

 are produced when the structure is sound. One 

 fibril, though but faintlv shown, is left bv itself 



Figure 395. T. faviis, from fragment of another 



valve, showing the same characteristics of torn 



structure. Magnified two thousand diameters. 



fibril. It is of the usual wavy 

 pattern. On each side is a 

 clear space, and, both abo\e 

 and below, the regular untorn 

 structure, showing how the 

 he.xagons are formed h\ other 

 fibrils. 



Figure 392 of the present 

 article (magnified three thous- 

 and diameters) is taken from 

 the centre of the saine val\< 

 of T. favits. and should prove 

 interesting both as an ex- 

 ample of high direct magnifi- 

 cation and for what it shows. 

 In two divisions the struc- 

 ture is torn away, two 

 fibrils are arranged in a 

 circular direction and be- 

 hind one, where marked, is 

 seen a series of white dots 

 similar to that we' shall find 

 directly in Coscinodiscus asteroniplniliis. Of course, 

 at another focus the dots would be black and the 

 enclosing structure white. 



Figures 393 and 394 are from the fragment of 

 another valve. Figure 397 showing the interspaces 

 almost denuded of fibrils, and Figure 392 the large 

 hexagons immediately underneath. The first Figure 

 should dispose once for all of the opinion that the finer 

 structure lies at the floors of the hexagons. (As a 



FlorRE 397. T.favus 

 fragment. Magnified 



Figure 396. The same as last, but at another focus, 

 showing that neither the size nor shape of the irregular 

 structure changes in passing from black dot to white. 



Stretching into space: in 

 another part, marked with 

 a X , the top covering is torn 

 away entirely; but upon focus- 

 ing down (Figure 392) the 

 hexagons are untouched. 

 Where the hexagons are 

 ruptured, also, is not the part. 

 .\ttention is called in this 

 last print to the large discs, 

 iharacteristic of this genus. 

 They correspond to a great 

 ixtent to the eye-spots in 

 the discoid forms, only much 

 larger. 



The next three figures, 395, 

 396 and 397, are froin the 

 fragment of another valve. 

 Figures 395 and 396 are the 

 same, the focus slighth- 

 altered. Figure 397, one view- 

 only, is from another part of 

 the same fragment. And here the writer wishes to call 

 attention again to certain peculiarities of structure. 

 He was ver\- much puzzled at this, because they did 

 not conform to his theory, and he could not say in 

 his heart : " So much the worse for the facts." It 

 will be seen, on reference, that Messrs. Nelson 

 and Karop speak of the perforations as circular, and 

 arranged for the most part in rows. Now, given a 

 membrane, in which are either stamped holes or 



from another part of the 

 two thousand diameters. 



