NA TURE 



537 



THURSDAY, OCTOBER 5, iS 



THE STUDY OF DIATOMS. 



An Introduction to the Study of the Diatomacea. By 

 Frederick Wm. Mills, F.R.M.S. With a Bibliography 

 by Julian Deby, F.R.M.S. (London and Washington: 

 Iliffe and Son, 1893.) 



F'EW forms in the organic world have been the sub- 

 jects of such close, constant and varied study as 

 the Diatoms. Their minuteness, their exquisite modes 

 of growth, development and multiplication in the living 

 state, and the beautiful refinement of symmetry and deli- 

 cacy of surface Chasing in their dead siliceous remains, 

 have made them the special objects of interest, admira- 

 tion, and often of serious study and research from cer- 

 tainly the dawn of this century until now. But there are 

 few studies of living objects, at least of those that are 

 extremely minute, that show more clearly that the real 

 difficulties presented by them are understood only by 

 those who thoroughly study them. It is the expert who 

 knows how little is known concerning this most interesting 

 if lowly group. 



If no other purpose were served by this book, it would 

 in a popular manner make this manifest. 



There can be no serious doubt that much of the value 

 that will attach to it as an "Introduction" is due to the 

 very accessible and useful form in which Mr. Julien 

 Deby's "Bibliography relating to Diatomology " has 

 been presented to the student. The work consists of 240 

 pages ; of these only forty-two are devoted to an expo- 

 sition of the nature and habits of the Diatoms proper. 

 There are three chapters relating to the collecting, the 

 mounting, and the microscopical examination of these 

 forms ; but the forty-two pages are supposed to tell us 

 all of importance that is known concerning these 

 beautiful Algae. Yet the Bibliography is enormous and 

 includes the work and judgments of some of the leading 

 naturalists of our century. 



As this volume only aims at being an " introduction " 

 to the study of these organisms, we have no right to 

 anticipate exhaustive treatment in any branch of the sub- 

 ject ; but we do not hesitate to affirm that the aim of its 

 author would have been more efficiently reached had 

 certain parts of his subject received a more liberal treat- 

 ment. 



No doubt the Bibliography opens to the amateur and 

 the student almost every channel of knowledge, and will 

 prevent him from attempting to repeat work already done, 

 or from exhausting himself on work that it is at present 

 more or less vain to attempt. But it would have been a 

 great advantage to have seen in a concise form much 

 that has been done in recent years. 



Thus we find less than three pages devoted to the 

 " Structure " of Diatoms ; what is said is interesting and 

 accurate ; but, even remembering the aim of the author, 

 we cannot consider it sufficient. It is quite true that no 

 great generalisation of diatom structure has been arrived 

 at ; and we venture to think that much time and patient 

 labour must be spent before it will be ; nevertheless, dur- 

 NO.1249, VOL. 48] 



ing the last ten years some admirable glimpses at the 

 wonderful architecture of these minute siliceous frustules 

 have been obtained, showing that these silicified cases 

 are not merely formed of two symmetrical valves united 

 to one another by means of two embracing rings which 

 constitute the connecting zone or girdle, and making 

 together an elegantly carved box in which the species 

 may be reproduced, but showing also that the most com- 

 plete structural principles are embodied in their internal 

 and external construction. 



These are certainly not complete studies ; but they do 

 exactly what the zealous amateur wants : show the 

 paths along which profitable study may be pursued. 



This will apply with even greater force to the almost 

 new branch of diatom work done in regard to "secon- 

 dary structure " in the siliceous frustule. To those for 

 whom this Introduction could be alone intended, few 

 things could have a larger interest than this. 



The nature of the extremely delicate " markings " of 

 diatoms has been so zealously pursued by amateurs and 

 microscopists generally, that it has brought upon them the 

 frequently merited reproach of "Diatomaniacs." None the 

 less it will be by the study of the perforations and physical 

 constitution of the siliceous frustules that we shall 

 ultimately obtain a true knowledge of their modes of 

 motion, and even some aspects of their physiology. It 

 would hardly have been supposed by those who wholly 

 neglect, or even despise the study of the " markings " of 

 diatoms that the wonderful "secondary structure" now 

 demonstrated in many of these frustules had any exist- 

 ence. It may now, however, be taken for granted that 

 every efficient manipulator possessed of a good micro- 

 scope has demonstrated that, ^.^., Coscinodiscus asterom- 

 phaltis is not only covered on its valves with the 

 beautiful areolae so long and so well known, but that 

 these areolre are in their turn delicately areolated. The 

 coarse areolations so long familiar to us are for the most 

 part approximately circular in outline ; but inside these 

 is a most delicately perforated membrane ; and that this 

 is related to the functions of the diatom there can be 

 but little doubt. 



Again it may be stated that these studies are incom- 

 plete ; that is so; and, moreover, they require good in- 

 struments, and good manipulation of them, for satisfactory 

 results ; but we believe that it is such matters that the 

 leisured amateur and the young student are most desirous 

 of knowing in order to find suitable lines for profitable 

 study. 



It is true that the very remarkable work of Dr. Flogel 

 on diatom sections, and some of his modes of operation 

 are referred to, but these represent a far higher and 

 more unusual class of research. The most elementary 

 student should know something concerning them, and 

 they are wisely referred to in this volume ; but they do 

 not compensate for the absence of efficient reference to 

 the class of work we allude to. 



The movement of diatoms receives careful treatment 

 in this treatise ; we believe, nevertheless, that more 

 recent results might with profit have been referred to. 

 The subject is in many senses one of the most difficult 

 in the range of Biology. The three principal explana- 

 tions, viz. endosmatic and exosmatic currents, the pre- 



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