April 4, 1901] 



NA TURE 



535 



axes ; or the parts of a molecule may oscillate about 

 their common centre of mass ; (7) All oscillations are 

 either ordered or unordered motions. 



The various types of oscillation are held by Dr. Fischer 

 to account respectively for chemical light-vibrations, 

 electric light-vibrations, heat, gravity, electric and mag- 

 netic phenomena. 



While Madame Royer's speculations on the nature of 

 things lead her to think that the laws of nature are never 

 disturbed by " that imaginary being called God, who has 

 no place in an autonomous universe," Dr. Fischer con- 

 cludes his paper with the quotation 



" Die Himmel erzahlen des Ewigen Ehre." 



We far prefer the spirit of the latter writer, who in the 

 course of his work clearly sees that theories of matter 

 can but be'approximate mechanical representations of the 

 truth. It is true that a good deal of progress has been 

 made of late years in the conception of elements and 

 media which reproduce more or less closely the physical 

 phenomena known to us ; but whether we regard the 

 universe as filled with a single medium and atoms as 

 singularities occurring in it, or regard everything, in- 

 cluding the ether, as built up of discrete atoms, a reduc- 

 tion of the number of varieties of atoms and media is not 

 necessarily synonymous with an advance in physical 

 theory. What is rather wanted is to reduce to their 

 minimum the number of fundamental hypotheses required 

 for the mathematical deduction of the physical pheno- 

 mena known to us. This was the spirit which actuated 

 Maxwell, and while since his time we have become more 

 and more familiar with molecules and the ether, it is 

 doubtful whether our advances in reducing their proper- 

 ties to mathematical formulae have been so great as they 

 ought to be. With the exception of Larmor, there are 

 few physicists now carrying on the work of Maxwell, and 

 there is, unfortunately, a growing school who conceal their 

 ignorance of the causes of things by referring everything 

 to " molecules " or " the ether," and endowing these with 

 new properties without troubling much if such properties 

 are reconcilable with those previously attributed to 

 them. What is equally important, as our theories of 

 matter advance, fresh properties become known to us, so 

 that as soon as we have climbed to the summit of one 

 hill, we see a still higher one ahead. G. H. B. 



ALLEGED HYPOSTOMIAL EYES IN THE 

 TRILOBITES. 



Researches on the Visual Organs of the Trilobites . By 

 G. Lindstrom. Kg. Svn. Vet. Akad. Handlg., Stock- 

 holm. Bd. 34, No. 8. Pp. 74 ; 6 plates. (1901.) 

 THIS memoir of 74 pp., illustrated by six most 

 beautiful plates, deals in reality with the joint 

 labours of the author whose name appears upon the 

 title-page and his talented assistant, G. Liljevall, to 

 whom the first detection of the central fact of the presence 

 of supposed eyes on the labrum (hypostome), the labour 

 of cleaning and preparing the specimens described, 

 and, above all, of making the original drawings (for which 

 no praise can be too high) are due. The material de- 

 scribed is mostly a rich collection preserved in the 

 Swedish . National Museum ; but it is explained, with 

 NO. 1640, VOL. 63] 



comment none too flattering, that "collections of foreign 

 species and the waste (vast) European and American 

 literature " have been taken into account. The work 

 opens with a short introduction, dealing mainly with the 

 detailed surface anatomy of the hypostome and the orient- 

 ation of the supposed hypostomial eyes, or "maculae," 

 as the authors name them, together with an account 

 of the first observations upon which, by comparison with 

 the cephalic eyes of the compound type, they were led 

 to regard the maculae of the facetted kind as visual in 

 function. There then follows a chapter upon the blind 

 Trilobites. A detailed dissertation upon the origin and 

 nature of the ridge hitherto designated the " eye-lobe," 

 " ocular fillet," or " Augen Leiste," and known by a 

 variety of other names, next follows ; and the authors, 

 finding that " in a long series of genera succeeding each 

 other it has no connection whatever with any eye," 

 prefer to term it the " facial ridge " ; and they subdivide 

 the blind species into series characterised by its presence 

 or absence. 



In the foregoing section much is made of the young 

 larvae of Olenellus, discovered by Ford and Walcott, 

 as furnishing a clue to the development of this facial 

 ridge, and of the fact that during the growth process of 

 the higher forms the pygidium follows the head region 

 in order of appearance, and that the intervening 

 " thorax " or body-segments are intercalary in origin. 

 Passing to detail concerning the head, Bernard's terms, 

 " rhachis " and " pleura " are preferably employed, and 

 in dealing with its anatomy a passing compliment is 

 paid to the Japanese embryologist, Kishinouye. Atten- 

 tion is next drawn to an important series of growth 

 stages of Liostracus, described by Brogger in 1875, but 

 generally overlooked, and from the study of these the 

 conclusion is reached that the developmental changes of 

 the head segments in the higher Cambrian and Silurian 

 forms are of a different order to those of the Olenellidae 

 and Paradoxidae, which Dr. Lindstrom would apparently 

 regard as representative members of distinct series ; 

 and the final result is arrived at that the earliest oculate 

 genus was Eurycare of the Olenellus schists, and that 

 Olenus and Parabolina were probably blind. 



The succeeding section is devoted to the consideration 

 of the eyes of the Trilobites, the detailed structure of 

 which the authors, with immense labour, have investi- 

 gated, by sections taken at various planes and by other 

 means at their disposal. They have been thus enabled 

 to distinguish four types of cephalic eye, which they 

 believe to have probably succeeded one another in the 

 following order, viz. the simplest or Harpes type, of 

 simple ocelli ; the Eurycarid, biconvex or lentiform type ; 

 the Megalaspid or prismatic type ; and the Phacopsid or 

 " aggregate " type — each of which is duly figured with as 

 much detail as is forthcoming, and in section as observed 

 for thirty-six species. Further detail under this head is 

 impossible in these pages ; and we pass at once to the 

 fuller consideration of the " maculae," or hypostomial 

 eyes so-called. 



Although the authors record these organs for some 136 

 species of thirty-nine genera, they state at the outset that 

 the genera in which they have found them lens-bearing 

 are relatively few, and that the lenses or " granules," even 

 where recognisable, have been found to be present only 



