706 SUMMARY OF CURRENT RESEARCHES RELATING TO 



wliicli I wish to put forward to better explain my views. In the] 

 greatest number of different types of Diatomaceje which I have repro- 

 duced and measured by microphotography, I ought to admit that in 

 examining certain species, although well-determined but placed in 

 different preparations, I have found some differences in specimens 

 of the same species, in regard to the number and fineness of the strife ; 

 nevertheless, when I have met with these differences, they have never 

 been considerable relatively and j^roportionally to their number, for 

 the difference has never exceeded 4. But at the same time I 

 declare most emphatically that up to the present time I have never 

 found the smallest difference wlien I have compared the frustules 

 which not simjily belonged to the same species but also to the same 

 stock. 



On these facts depends the validity of all the deductions which 

 can reasonably be drawn from the constancy of the fineness of the 

 strife on the large and small frustules belonging to the same species 

 and the same stock. I have sjioken of these deductions in the paper 

 entitled " Nuovi argomenti, &c." I have there referred to a very 

 pure gathering which I made near the fountain in the " Fields of 

 Annibal," on Mont Cavo near Rocca di Papa, which was solely com- 

 posed of myriads of frustules of Pinnularia dauroneiformis Sm. var. 

 latialis, a variety which I thouglit myself justified in establishing on 

 the ground of the very great difference in the number of the strife in 

 the form from Mont Cavo, which was 1900 to the millimetre, and 

 in tlie typical form of Smith, which has not more than 1200 in the 

 same space, a difference which exceeds ^-, all the other characters 

 remaining absolutely identical. On this occasion I have deduced 

 from the constancy in the form of the strife on the largest and the 

 smallest frustules in this collection : (1) That at least in this case 

 multiplication did not take place by tcmnogenesis or division, for, on 

 the hypothesis of the gradual diminution of the valves and frustules, 

 resulting from the encapsulemeut of the latter, the strife ought in the 

 same proportion to become finer and finer, if the very explicit opinion 

 of Dr. Wallich is true, viz. " that the number of strise in a fractional 

 part of the valve undergoes precisely the same variation as the size of 

 the valve; " (2) That the auxesis, the augmentation of the size of the 

 frustules, must take place by the bilateral addition of new strias, and 

 consecutive dilatation of the bands or zones which unite the valves ; 

 (3) That thus the diatom, although invested with a siliceous coat, is 

 the object of a gradual develoi3ment and distension because the silex 

 is probably found in a combination with cellulose,* in which it 

 replaces the carbon, a substitution the possibility of which is demon- 

 strated by the labours of the chemists Friedel and Ladenbourg. 

 In support of the second part of tliis deduction, that is, that in the 

 Diatomacefe the auxesis must take place by bilateral addition of new 

 strife and not by perispherical increase as in the Crustacea, I refer to 

 another argument. I have pointed out above that in the collections 

 formed of a single species, there are alvvays found large and small 



* Mon. Micr. Journ., viii. p. 194. 



