352 Dr. G. C. Wallich on the Structure of 



on every kind of microscopic research, and in this sense only do 

 I consider it worthy of serious investigation. 



In a paper " On the Structure of the Valve in the Diatomacese, 

 as compared with certain Siliceous Pellicles produced artificially 

 by the Decomposition in moist Air of Fluosilicic Acid Gas 

 (Fluoride of Silicium) "*, Prof. Max Schultze, after stating his 

 views regarding the mode of formation and intimate structure of 

 the pellicles referred to, enters on the special point towards which 

 his investigations seem to have been directed, namely, the deter- 

 mination of the true character of the markings in Pleurosigma 

 angulatum. Prof. Schultze alludes to the conflicting opinions 

 entertained by English microscopists on this subject, and, whilst 

 citing Carpenter (undoubtedly the highest of the British autho- 

 rities on any question of microscopy) and, with him, many other 

 observers who support the view that the markings of the valve of 

 this Diatom consist of hexagonal depressions, associates my name 

 with that of my friend Mr. Norman, of Hull, amongst the advo- 

 cates of the contrary opinion, namely, that these markings con- 

 sist of pyramidal elevations f. In the abstract of Prof. Schultze's 

 paper already alluded to, it is stated that, " so far as the nature 

 of the markings on the Diatomacese is concerned, opinions may 

 not at the present day be so much divided in this country as that 

 author appears to think ; " and marked attention is for the 

 second time drawn, by the Editors of the ' Microscopical Journal,' 

 to an observation made by Mr. Wenham during the discussion of 

 my paper on these markings, read before the Microscopical So- 

 ciety in March 1860, to the effect " that, with an object-glass 

 of his own construction, having a focal distance of about -_2^th of an 

 inch and a large aperture, he had ascertained beyond doubt that, 

 in P. angulatum and some others, the valves are composed wholly 

 of spherical particles of silex, possessing high refractive proper- 

 ties ; and that he showed how all the various optical appearances 

 in the valves of the Diatomacese might be reconciled with the 

 supposition that their structure was universally the same".|. 

 As the hexagonal-depression structure of the valve in P. angulatum 

 rested almost exclusively, up to that period, on evidence adduced 



* Verhandl. d. Naturhist. Vereins der preussisch. Rheinlande u. West- 

 phal. Jahrg. xx. p. 1. See an abstract of this paper published in the 

 Quarterly Journal of Microscopical Science for April 1863. 



t See papers " On the Markings of the Diatomacese in common use as 

 Test-Objects," published in the Annals and Magazine of Natural History 

 for February 1860 ; and "On the Development of Structure of the Diatom- 

 Valve " (read before the Microscopical Society in March 1860, and published 

 in the Transactions), by G. C. Wallich, M.D., &c. 



X See note appended to abstract to Prof. Schultze's paper, and note 

 appended to the above-named paper by me, published in the Transactions 

 of the Microscopical Society, Quart. Journ. M. S. vol. viii. p. 145. 



