Researches on the visual organs of the trilobites

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 described is mostly a rich collection preserved in the. Swedish National Museum; but it is explained, with 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 orientation of the supposed hypostomial eyes, or “maculæ,” 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 maculæ 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.Researches on the Visual Organs of the Trilobites