J. DEBY ON THE STRUCTURE OF THE DIATOM VALVE. 317 



to the hexagonal cells. Mr. Christian's specimen of Triceratium 

 is the first example of the entire separation of the laminae which I 

 have met with in that species." His later papers confirm his pre- 

 vious opinions. 



My friend, Dr. H. Van Heurck, of Antwerp, in his synopsis of 

 Belgian Diatoms * supports the views of Mr. Cox. 



Judging from the beautiful plates of the genus Triceratium in 

 the last numbers published of A. Smidt's Atlas, I believe this 

 acute observer and admirable draftsman must hold similar opinions 

 as Mr. Cox and Van Heurck. 



Last year Dr. G. C. Wallichf refers to the views of Dr. 

 Flogel and of Mr. Cox, and tries to oppose, upon physical grounds, 

 and not without force, the opinions of the latter author when he 

 states that the alveola are in all cases hermetically sealed cavities. 



From all I have said above, it may be inferred that I reject the 

 " porous theory " of the Diatom valve if the orifices are to be 

 understood as perforating the whole substance of the valve so as to 

 allow of contact between the living matter of a Diatom and the 

 exterior through properly so-called, and visible, apertures. I con- 

 sider the " eye spots " to consist in the living valve of an organic 

 cuticle which is seldom highly silicified. This cuticle is very 

 readily destroyed, in which case the orifices in the thickness of the 

 valve become open at one end at the place where the " eye spot ' 

 existed, while in all cases where great corrosion has not taken 

 place these cavities or areolae in the valve are closed at the 

 bottom by a stretched and continuous siliceous film of considerable 

 thickness as compared with the upper one, and which precludes 

 the protrusion of protoplasmic filaments and all direct admission of 

 external solid substances into the cavity of the frustule. 



I regret I cannot concur in all that has been lately said on the 

 subject of the orifices in the Diatom valve by some of the sharpest 

 and certainly most skilful, if not the most philosophical, of micro- 

 scopical manipulators, both at the Quekett Club and at the Royal 

 Microscopical Society's meetings. 



To all microscopists interested in the final solution of this long- 

 debated question, I tender an invitation | to come and satisfy 



* " Synop. des Diat. de Belgique," Text., p. 35. 



f u Engl. Mech.," xl, 1885, p. 496 ; and '« Jourl. R. Micr. Soc," 1885, 

 Vol. v, p. 286. 



X Microscopists will generally, when I am not, as occasionally happens, 

 absent upon professional business, find me at home from 10.30 a.m. to 5 p.m., 

 and from 7 to 10 p.m. on Saturdays. 



