J. DEBY ON THE STRUCTURE OF THE DIATOM VALVE. 309 



as the mixtures have become hard, thin sections of them can be 

 made in the same way as with ordinary rock. If sufficient care is 

 taken it is not difficult to obtain sections of a less diameter than 

 the areola of a Triceratium or of a Coscinodiscus. These sections 

 have been corroborative of my general conclusions as detailed 

 further on. 



II. 



I have repeated, on several occasions, the experiment first tried 

 by the late Prof. J. W. Bailey, of West point, as early as 1851, 

 namely, of dissolving the diatoms, under the microscope, in 

 hydrofluoric acid. My results have been identical with those 

 obtained by this very excellent observer. Prof. Bailey's paper 

 not being easily accessible, as it was published in the " American 

 Journal of Science and Arts," 2nd Series, Vol. xi, I have thought 

 that a reproduction of it here might not prove out of place on 

 account of the interesting demonstrations it gives of various 

 points in diatom structure. Some of these, however, relating to 

 the nodules and rachis, are at the present day acknowledged by all 

 naturalists, and as such are somewhat irrelevant with the subject 

 under discussion. 



" On the real nature of the so-called i orifices ' in Diatomaceous 

 shells. — It is well known to naturalists that several of the most 

 distinguished writers on the Diatomaccas have asserted the 

 existence of ' apertures,' ' orifices,' or mouths in the ventral sur- 

 faces of many shells belonging to this family, and have even 

 founded classes and genera upon the supposed presence of these 

 openings. Some years ago I expressed in this Journal my dis- 

 belief in the existence of the apertures in the following words : — 



" ' There are three rounded spaces on each of the ventral faces 

 (of Navicular), which, I think, have been mistaken for openings 

 but which appear to me to be thicker portions of the carapace.' 



" This opinion was founded upon a careful observation of various 

 fragments as seen in clean fossil specimens, and I still think that 

 by the inspection of such fragments full evidence of the truth of 

 my opinion may be obtained. I now offer proof of another kind 

 which removes all doubt, and shows that these markings are 

 neither apertures nor depressions, but are in reality the thickest 

 parts of the shell. If the shells are placed in dilute hydrofluoric 

 acid and watched by aid of a microscope as they gradually dissolve, 

 the thinnest parts, of course, dissolve first, and apertures, if any 



