54 



THE AMERICAN MONTHLY 



[March, 



recent observations of the gentlemen 

 named above, and we have recently 

 received a pamphlet of seventy-three 

 pages and four plates, taken from the 

 Annales de la Soc. beige de Alicr.^ 

 which presents the results of their 

 work in a complete form. 



The diatoms studied were princi- 

 pally those of the cement stone from 

 Jutland, which is a calcareous rock 

 containing an abundance of organic 

 remains — diatoms, protozoa, etc. It 

 also contains some pyrites, which is 

 occasionally deposited within the 

 frustules, and assists in the elucida- 

 tion of their structure. 



The stone is carefully selected, and 

 sections are ground exceedingly thin 

 for examination. The diatoms are 

 found to be disposed in layers, which 

 enable the sections to be made in the 

 desired direction with reference to the 

 frustules. By making the sections 

 parallel with the stratification, sec- 

 tions more or less inclined to the 

 plane of the frustules, or parallel to 

 it, are obtained. Sections at right 

 angles give what are termed normal 

 sections. The sections were mounted 

 in the usual manner, in balsam, or in 

 some cases they were first decalcified 

 and isolated. 



The structure of Coscinodiscus 

 oculus Iridis has long been the sub- 

 ject of discussion. Mr. J. W. Ste- 

 phenson found that the silicious frus- 

 tule consisted of two layers, w^hich 

 could be separated, both apparently 

 perforated. The study of the sections 

 carried out by Messrs. Prinz and Van 

 Ermengem fully sustains this view, 

 showing in the centre of each of the 

 hexagonal areoles a minute pore at 

 the bottom of a depression. Mr. 

 Stephenson's conclusions w^ere based 

 upon the study of the appearances of 

 the frustules when mounted in differ- 

 ent media. It is interesting to find 

 them verified by a totally difterent 

 and apparently a conclusive method 

 of examination. 



Diatoms coated or filled with pyrites 

 from the London clay were also stud- 

 ied, and they have materially aided 



the progress of the investigation. In 

 alluding to these, we are reminded of 

 an amusing story about them. It 

 was, and we believe still is, a diffi- 

 cult matter to obtain good specimens 

 of the London clay diatoms, which 

 are so perfectly coated with the pyrites 

 that they have a beautiful appearance, 

 like polished gold, under the micro- 

 scope. Mr. A. C. Cole mounted a 

 few of them, and some sceptical indi- 

 vidual in London accused him of 

 " electrotyping" the diatoms ! How- 

 ever, Messrs. Prinz and Van Ermen- 

 gem have found those diatoms of 

 great sei^vice to them in their investi- 

 gations. 



The investigations of these gentle- 

 men are exceedingly meritorious, and 

 desei-ve to be widely known. Unless 

 there are some radical errors in their 

 methods and observations, it must be 

 regarded as an established fact that 

 the silicious coverings of the diatoms 

 they have studied are perforated. 

 Accordingly, the frustules of Coscin- 

 odiscus^ Trinacria^ Pinnularia^ are 

 perforated. In another place, how- 

 ever, is published the first of several 

 articles by the Hon. J. D. Cox, who 

 has arrived at results directly contra- 

 dictory to those of the authors men- 

 tioned by a totally difterent method 

 of observation. The question, there- 

 fore, is still an open one, and offers 

 an opportunity for further observa- 

 tion. 



Supposing it to be finally decided 

 that the frustules are perforated, it 

 remains to be seen whether the cell- 

 contents can be extruded through the 

 minute apertures, as Dr. Carpenter 

 has suggested may be possible. 



As some of our readers may be dis- 

 posed to repeat the obsei"vations and 

 prepare sections of diatoms, we may 

 here suggest a plan for imbedding the 

 diatoms from fresh gathei'ings, which 

 we intend to apply to another branch 

 of investigation. It is to prepare an 

 artificial calcareous rock from a mix- 

 ture of finely-ground lime and clay, 

 making a kind of hydraulic cement, 

 with which the diatoms may be min- 



