892 



SUMMARY OF QUERENT RESEARCHES RELATING TO 



Fig. 155. 



the valve crossed sometimes by a broken line, like that drawn by 

 M. Pfitzer, sometimes by a more or less oblique line. 



These alterations must be due to the fact that the balsam, intended 

 to consolidate the frustules, does not penetrate into their interior. 

 They therefore remain empty, and their finest details not being 

 sufBciently supported, they do not resist the polishing. Similar 

 difaculties have probably obliged M. Pfitzer to represent diagram- 

 matically the result of his observations on a certain number of 



At last, in one of the preparations, I came across a rather thick but 

 unbroken section of an individual of great size. It is at right angles 

 to the long axis of the diatom, and consequently gives a normal 

 section of the raphe, taken in the neighbourhood of the central 



nodules, that is in the thickest 

 and most resisting portion of the 

 frustule, fig. 155. 



The complete and minute de- 

 scription of the structural details 

 of Pinnularia, given by M. Pfit- 

 zer, can be applied point by point 

 to this figure, drawn entirely after 

 nature. I refer therefore to this 

 description, and I will only here 

 dwell on the slight diiference 

 which may exist between my draw- 

 ing and his. 



The section of the raphes pre- 

 sents at this point the appearance 

 of rather large slits, penetrating 

 perpendicularly the interior of the 

 a Eaplie, b c d rib, e bevelled edge of frustule, where they terminate in 



two curves in opposite directions 

 to one another. 



I have already said that I have 

 not been able to obtain satisfactory 

 sections of this organ in a region 



the valve, / CL'ntral nodules, g connec 

 tives. X 1500. (The black parts have 

 a brown colour by transmitted light.) 

 Dimensions — Height and width of the 

 frustule (outside) 27 and 28 /j.. Thick- 

 ness of the valve at a 3 • 3 jU, at 6 and d 

 Width of the raphe • 4 /x. Width 



Of the nodules at the base 7-5^. Height more distant from the central 

 of the nodules, not including the thick- nodules, and where it appears to 

 ness of the valve, 3-9 m- Thickness of be placed obliquely. I think, with 

 the connectives 0-5 m- M. Pfitzer, that the raphidian fis- 



sure is more and more inclined at 

 this point to resume the vertical position towards the terminal nodules. 

 The asymmetry of the central nodules is more apparent, and they are 

 also more prominent than those which the author has drawn. I have 

 not seen any solution of continuity in these nodules (Schumann) ; 

 they appear perfectly solid. The section of the connectives and the 

 slight displacement which they have accidentally undergone, confirms 

 the opinions of Pfitzer on their mode of attachment, which is very 

 common in different genera of diatoms ; but I have not succeeded in 

 finding the rather deep furrow which, in his opinion, surrounds the 



