ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1)43 



proper attention to the coircction of tlie objective will enable us to 

 detect it in tbe robust shells found in the Nottingham earth. 



" In the Nottingham slides all the parts of the gigantic disks are 

 increased in size and thickness, and upon examining the interior 

 plate we find within the hexagonal tracing : 1st, a narrow circle so 

 thin as to be scarce distinguishable in colour from the empty field ; 

 2nd, another narrow ring of pinkish colour, evidently thicker than the 

 last; 3rd, another nearly colourless ring; and lastly, a small central 

 part of appreciably pink tint. Nearly every broken valve will give 

 some examples of the inner lamina projecting beyond the outer, and 

 a patient examination will soon find examples in which the fracture, 

 passing through the eye-spot so as to break off only an outer segment 

 of, say, one-third its area, leaves the inmost spot, the pink ' pujjil ' of 

 the eye, intact. I have verified this so often as to be able to assert it 

 categorically. ... As to the upper film, the same prejiarations give 

 abundant evidence of its existence." 



J. Deby also,* while not disputing that what the authors describe 

 and figure did actually exist in their sections, nevertheless considers 

 that their deductions are entirely erroneous, which has arisen in 

 consequence of their having studied not living but fossil forms, which 

 have lost not only the purely membranous jiarts but also a certain thick- 

 ness of the siliceous layer. The dissolution of the silex of diatoms 

 takes place with great facility, as he shows by an experience which 

 occurred to himself, where some Epithemia in a vessel of brackish 

 water with Synedra were found at the end of two months to have been 

 entirely dissolved, doubtless furnishing the Synedra with the silex 

 which they required for the formation of their valves. Mr. Deby has 

 numbers of diatoms belonging to genera which the authors describe 

 as having perforations, which undoubtedly have septa which close at 

 each end the supposed orifices. 



Structure of the Diatom-Shell.t — Dr. J. D. Cox gives the results 

 of a series of repeatedly verified observations on this subject, using 

 both transmitted and reflected light. With the former he preferred 

 balsam slides illuminated by a narrow central pencil, and for reflected 

 light the vertical illuminator was found invaluable. The objectives 

 were of the largest aperture. 



Triceratium favus he finds is formed of two laminaB connected by 

 an hexagonal network, of which the areolae are about as deep as the 

 diameter of the hexagons. The inner of these laminae is finely dotted 

 with lines of puncta9 radiant from the centre of the triangle, the outer 

 lamina being very thin over the centre of each hexagon, to which it is 

 firmly connected by the walls of the areolfe, which arc thickened so 

 as to give a hemispherical interior form to the upper end of each. 



Eupodiscus argtis may be considered, typically, as having a sub- 

 hexagonal arrangement of areolae in the outer lamina of the valve, 

 the walls of these areolao being extraordinarily thickened outwardly, 

 making a rough honeycombed surface. The inner lamina has its 



• Journ. (Ic Microgr., viii. (1884) pp. 22H-']0. 



t Amcr. Mon. Micr. Journ., v. (1884) pp. 45-9, 06-9, 85-9, 104-9. 



