66 



THE AMERICAN MONTHLY 



[April, 



pie space beneath the stage for ap- 

 paratus. It is an elaboration of the 

 plan of Mr. George Wale, and a sim- 

 plification of the more recent design 

 of Mr. Wenham as applied in the 

 large stand of Messrs. Ross & Co. 

 The illustration renders a full descrip- 

 tion unnecessary. This stand will be 

 figured in the new catalogue to be is- 

 sued by Messrs. Bausch & Lomb in 

 the course of a few months, which 

 will also contain a number of new in- 

 struments and devices not heretofore 

 known. 



Structure of the Diatoiii-shell.-II. 



BY JACOB D. COX, LL. D., F. R. M. S., 

 PRES. AM. SOC. OF MICR. 



When the preceding article went 

 to the printer I had not yet had the 

 opportunity of reading more than a 

 synopsis of the investigations made 

 by MM. Prinz and Van Ermengem, 

 of the Belgian Society of Microscopy, 

 upon sections of the Jutland cement- 

 stein and the diatoms contained in it. 

 The text of their interesting papers 

 will stimulate others to repeat their 

 examinations and to prove the alleged 

 advantages to be gained from their 

 method of investigation. The doubts 

 as to its value, which have been com- 

 mon among students of diatoms, have 

 been based upon the belief that the 

 friable character of the sedimentary 

 rocks is such that it was hardly to be 

 expected that sections thin enough 

 could be successfully made, or that 

 the extremely delicate silicious films 

 of diatoms would withstand the grind- 

 ing. A stimulus to try this field of 

 inquiry more thoroughly is, there- 

 fore, very welcome, even if we do 

 not find in the papers of the Belgian 

 naturalists any conclusive evidence 

 upon points yet unsettled. 



Their investigations have been 

 chiefly made upon Coscinodiscus 

 oculus zridis, Cose, excentricus ( Sytn- 

 bolophora Trinitatis of the Moller 

 type-plate), Trinacria regina., Tri- 

 ceratiumfavus., and upon allied forms 

 found in the London clay. M. Prinz 



had previously written upon the same 

 subject, including some investigations 

 upon sections of Pinnularia. Anal- 

 ogous work had been before attempt- 

 ed by MM. Flogel and Pfitzer. 



So far as these investigations lead 

 to the conclusion that the shells of 

 these larger diatoms, having discoid 

 or triangular forms, consist of two 

 laminae, in the outer of which are 

 hexagonal or circular areolae, the re- 

 sult is corroborative of views often 

 expressed by investigators who have 

 studied the subject. The point upon 

 which MM. Prinz and Van Ermen- 

 gem regard their observations spec- 

 ially decisive is that the exterior lam- 

 ina is wholly made up (in the diatoms 

 with hexagonal marking) of the honey- 

 comb structure, entirely open at the 

 top of the alveolas, and that the inte- 

 rior lamina only partially closes these 

 openings, being itself perforated by 

 circular holes at the bottom of each 

 of the hexagons. These holes appear 

 to them to be bounded by a wall like 

 a section of tube which projects a 

 little way through the lamina both 

 outwardly and inwardly. 



This conclusion is so decisively and 

 explicitly contradicted by the exami- 

 nation of these valves by other means 

 as to increase rather than diminish 

 our doubts of the value of sections 

 prepared as these have been. The 

 difference is so radical, and so easy 

 to test, that it challenges at once the 

 attention of all who are accustomed 

 to the use of the microscope. 



In the fii'st of the plates which il- 

 lustrate the paper by those gentlemen 

 is a figure of the interior plate of Cos- 

 cinodisctis showing the ' eye-spots.' 

 These are, by measurement, more 

 than half the diameter of the hex- 

 agons. In Triceratium favus the 

 hexagons are usually four or five to 

 the thousandth of an inch, and the 

 'eye-spot' or perforation should, 

 therefore, have a diameter of at least 

 .0001 -inch. But an amplification of 

 only a hundred diameters would make 

 this .01 -inch, and it should, there- 

 fore, be easily seen with any good \ 



