NOTES ON THE STRUCTURE OF THE DIATOMACE. 75 
man says that decidedly they are canals... .. And in the 
Aulacodisci this may be by means of the processes which are 
apparently perforate ; but in the Triceratia, Coscinodisci, etc., I 
think Mr. Deby’s suggestion, that it takes place at the margins of 
the connectives, is probably correct. The latter opinion is most 
probable, and the opinion I am inclined to hold. 
C. Gunther’s photographs show openings in P. axgulatum, Dr. 
Woodward’s photographs show elevations, and much of the dis- 
puting about spherules, &c., may be accounted for by alterations of 
the light upon or through the object, giving different appearances 
to the observer, also by the person, either drawing or photograph- 
ing an appearance without properly understanding the structure of 
the object he is at work upon. 
Fig. 34. Evidently a drawing of the central nodule of Pinnularia. 
I have no remarks upon it at present, not having seen that view of 
a diatom. ‘The original drawing is by Dr. Walker Arnott. 
REFERENCE TO FIGURES. 
Fig. 25. Oblique section, Coscinodiscus oculus tridis. M. Prinz. 
Fig. 26. Portion of valve, Coscinodiscus oculus tridis, jzin.  E. 
W. Burgess. 
Fig. 27. Section of Piznularia, shewing cavities. Dr. W. Arnott. 
Fig. 28. /innularia (portion of broken valve) single layer septa 
broken. W. A. 
Fig. 29. Pinnularia (broken valve) shewing alternating ribs and 
cavities. E. W. B. 
Fig. 30. Cross section of Pleurosigma angulatum, J. H. Flogel. 
Fig. 31. Cross section of Pleurosigma Balticum. J. H. Flogel. 
a. Depth. 
é. Midrib. 
c. Flat poreless stripe. 
e. Connections of the valve with the cingulum or connecting 
membrane. 
cd. Chlorophyll. 
Fig. 32. Enlarged portion of Fig. 30. 
Fig. 33. Enlarged portion of Fig. 31. 
Fig. 34. innularia, median line (nodule). Dr. W. Arnott. 
Notre.—Of the so-called areole in Coscinodiscus an example 
may be taken. Dr. Griffin of Bristol discovered, and has shown 
to the writer that the areolz (?) of the Coscinodiscus excavatus, 
Fossil earth, Newcastle, Barbadoes, if viewed in the same manner 
as the beetle’s eye, will give a figure for each spherule or areola. 
Query,—are not the areolz lenticular ? 
