788 SUMMARY OF CURRENT RESEARCHES RELATING TO 



organisms has increased. Accordingly it is not astonishing that an 

 identical form or type has often been distiuguished by different names, 

 whilst forms different in appearance, and consequently known under 

 different names, are now recognized, after more attentive observation, 

 as belonging to one and the same species, and must consequently be 

 united under the same name. But this constitutes the most ungrateful 

 and arduous task to which we can devote ourselves. It is necessary 

 to know the value of the characters by virtue of which one form may 

 be entitled to be recognized as a specific type, and to eliminate those 

 which may not be equally legitimate. It is thus that we may be able 

 to terminate the confusion which reigns in the nomenclature of the 

 Diatomacete, and which forms the greatest obstacle to those who have 

 attempted to undertake theu' study. 



But what are to be the rules to be followed in so delicate a 

 research ? in other words, what are the diagnostic characters of the 

 DiatomacesB by which we may distinguish them from one another 

 specifically ? Such is the question which I proposed to myself when 

 I undertook to study seriously this interesting order, and that is the 

 subject which has kept me the longest time in suspense. In fact, 

 every one admits that there is nothing more difficult in nature than 

 the determination of species and the fixing of their exact limits, and 

 some have founded on this difficulty an argument for denying the 

 existence of these limits. Without dwelling on the absurdity of such 

 a doctrine, which would annul at a single stroke the work of our pre- 

 decessors in the study of natui-e, and would destroy science itself, I 

 will show how the ordinary difficulties in the determination of specific 

 characters have been increased by the extreme smallness of the 

 organisms, in consequence of which it will never be possible to isolate 

 a living form, to watch its successive evolutions, and to determine thus 

 the independent characters of the organic evolution. Such characters, 

 recognized as constant and invariable, would constitute bases for 

 establishing the scientific characteristics and determining the distinct 

 and autonomous types. 



In such a state of matters, and awaiting the time when the means 

 of making a diatom grow in a narrow cell shall have been discovered 

 (as the mycologist makes the lower fungi grow in a moist chamber), 

 let us see what are the characters which these wonderful organisms 

 present — such of the characters as provisionally at least may serve 

 for the determination of the species. It will be wise to occupy our- 

 selves ^nth only one point at a time (when several present themselves 

 which are equally difficult), and we will content otu'selves with deal- 

 ing with striation, which distinguishes nearly all diatoms, and which 

 forms the most beautiful and most curious part of their ornamen- 

 tation. This striation is precisely that which most strikes the 

 attention of the observer, and on that account, as soon as ever the 

 Diatomaccaj were studied and described, the striation was the first 

 point that w^as noted, and then an endeavour was made to determine 

 its fineness by calculating how many strife are contained in a given 

 space, as in the y^^ of a millimetre. 



So long as the diatoms were not too small, and above all, that the 



