ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 941 



which fulfilled that office. To this Dr. Van Ermengem replied that 

 he " did not at all refuse to admit the existence of organic membranes 

 covering the perforations." 



Dr. J. D. Cox, in a criticism * of MM. Prinz and Van Ermengem's 

 paper, considers that their conclusions are " so decisively and explicitly 

 contradicted by the examination 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 first of the plates which illustrate the paper is a figure of 

 the interior plate of Coscinodisciis showing the ' eye-spots.' These 

 are, by measurement, more than half the diameter of the hexagons. 

 In Trlceraiium 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 in. But an amplifica- 

 tion of only a hundred diameters would make this -01 in., and it 

 should, therefore, be easily seen with any good 2/3 objective. As a 

 matter of fact, the ' eye-spots ' in the sei^arated inner plate of Coscino- 

 discus Oculus Iridis are so easily seen with a 4/10 objective and a 2-in. 

 ocular, that I am in the habit of using this glass on the double nose- 

 piece as a ' finder ' when studying that shell in the large variety 

 found in the Nottingham and Calvert County deposits. There- 

 fore, in an opaque preparation of this shell, or of Trlceratium favus, 

 since we are able not only to get an amplification of 400 or 500 

 diameters by the use of high oculars with the glasses named, but by 

 using a 1/4-in. with long working distance may considerably increase 

 the magnifying power, the supposed holes in such shells are far within 

 the limit of common observation by reflected light, and should easily 

 be seen in such slides as Moller's opaque Cuxhaven diatoms which I 

 have already referred to. The truth is, however, that with trifling 

 care in the manipulation of the light, the continuous surface of the 

 inner lamina of T. favus may be seen with a clearness which defies 

 all scepticism, and if the glass is a good one, there need be no great 

 difficulty in seeing upon its surface the finer system of dots which is 

 independent of the hexagonal marking, as in the case of Eujpodiscus 

 arijus also. The outer lamina will also be found continuous. There 

 is no room for illusion in this matter. Broken shells are easily found, 

 and some with holes broken in them, and the difference between a 

 plane surface and a solution of continuity is too plain to be doubted. 

 . . . Whether the inner or the outer plate of the valve is examined, 

 the closing of the hexagons by a film is as apparent as in examining 

 with the naked eye a real honeycomb which the bees have capped 

 with wax." 



Dr. Cox then describes a confirmatory experiment in which use 

 was made of reflected and transmitted light at the same time. The 

 object was a Coscinodiscus " having one of the laminae in part broken 

 away. It fortunately turned out, also, to be with the convex side up, 

 and enabled me to make what I must regard as an experimentum crucis. 



* Aiucr. Mon. Micr. Journ., v. (1881) pp. 66-D. 



