Abstract
The Quarterly Journal of Microscopical Science, for July, 1893, contains:—On the morphology and physiology of the brain and sense-organs of Limulus, by Dr. W. Patten (Plates 1 to 5). Some two years ago the author published a paper in the Quarterly Journal of Microscopical Science calling attention to many striking resemblances between Arachnids and Vertebrates, and maintaining that the latter are descended from a great group of the former, in which he included the Arachnids, Trilobites, and Merostomata. Attention was called to the evidences of relationship as shown in the invaginations which in insects give rise to the optic ganglia, and in scorpions and Limulus become so extensive as to enfold not only the optic ganglia but the eyes and the forebrain as well. A cerebral vesicle is thus formed, from the floor of which arise the forebrain and the optic ganglia, and from the roof a tubular outgrowth, at the end of which lie the inverted retinas of the parietal eye. Such a condition is to be found only in Arachnids and Vertebrates, and the author thinks it affords as trustworthy evidence of relationship as the presence of a notochord or of gill-slits. Other relationships were indicated between the lateral eyes in Limulus and Vertebrates, between the cartilaginous endocranium in Arachnids, and the primordial cranium of Vertebrates, between the subneural rod in scorpions and the notochord, and in the correspondence between the neuromeres and nerves in Arachnids and Vertebrates. To this long array of evidence the author now adds others: identifying nearly all the important lobes and cavities characteristic ot the Vertebrate forebrain in the forebrain of Limulus; showing that the coxal sense-organs are gustatory, and correspond to the supra-branchial sense-organs of Vertebrates, and describing a remarkable organ in Limulus, which has all the characteristic morphological features of the olfactory organs in Vertebrates. The author believes that it may now be regarded as beyond any reasonable doubt that the Vertebrates are descended from the Arachnids. The very interesting palæontological aspect of the subject is promised in a separate memoir.—On the structure of the pharyngeal bars of Amphioxus, by Dr. W. Blaxland Benham (Plates 6 and 7), gives a detailed account of the tongue (or secondary) bar in Amphioxus, and institutes a comparison between it and the primary bar, and there is a résumé of the observations of recent observers and an account of certain abnormal bars.—On the perivisceral cavity in Ciona, by A. H. L. New-stead, B.A. (Plate 8). The author found (1), that there are no communications between the perivisceral cavity and the atrial cavity (such as were described by Kupffer, though denied by Roule); (2) that definite communications exist between the perivisceral cavity and the pharynx, and as these openings occur in the same position as the orifices described by Kupffer, it is probable that the supposition of van Beneden and Julen is correct, that the orifices observed by Kupffer open into the perivisceral and not into the atrial cavity. The perivisceral cavity is regarded as a specially modified epicardium, which has become greatly enlarged.—On the early stages in the development of Distichopora violacea, with a short essay on the frag-mentation of the Nucleus, by Dr. Sydney J. Hickson (Plate 9). In this paper we have first an account of the early stages of the development of Distichopora violacea from material collected by the author in North Celebes and by Prof. Haddon in Torres Straits; then an account of the formation of the germinal layers in the Cœlenterata. A sketch of the developmental histories, as known up to the present, is given, with the typical invaginate gastrula at one end and the multinucleated plasmodium at the other; and, lastly, the important question of the “fragmentation” of the Oosperm nucleus is very ably and judiciously discussed, the following conclusions from the evidence adduced being drawn: (1) Fragmentation of the nucleus is a normal method of nuclear division, and is not always a sign of pathological change; (2) in many cases where the nucleus is supposed to disappear, there is, as a matter of fact, only a minute fragmentation; (3) that fragmentation only occurs when there is no cell division; and (4) that karyokinetic division of the nuclei is caused by the forces in the cell protoplasm which bring about the division of the cytoplasm. The phenomena of pluripolar mitosis may afford examples of intermediate types.
Article PDF
Rights and permissions
About this article
Cite this article
Scientific Serials. Nature 48, 332–333 (1893). https://doi.org/10.1038/048332a0
Issue Date:
DOI: https://doi.org/10.1038/048332a0