Oct. g, 1884] 



NA TURE 



575 



Dr. G. E. Dobson regarded this muscle as a rudimentary 

 vestige of a muscle found in all the lower animals, by the use 

 of which they are enabled to draw in their head and forelegs 

 when they erect their spine. 



On the Mutual Relation of the Recent Groups of JEchinoder?ns t 

 by Prof. A. M. Marshall. — Of these there were four groups, the 

 common starfish, brittle starfish, sea-urchins, and holothurians. 

 He said the nerve-system was originally derived from the skin. 

 In some animals the nerve system sank below, in others it re- 

 mained near the skin, these latter being in a more primitive 

 condition than those in which the nerve-system had sunk down. 

 Prof. Moseley characterised the paper as very valuable, having 

 fully borne out all the discoveries of Prof. Carpenter, whose 

 advancing age had prevented his being present. 



A paper On the Fatal Membranes of the Marsupials, by Mr. A. 

 H. Caldwell, who was sent to Australia by the British Associa- 

 tion to investigate certain interesting biological questions, was 

 read, in his absence, by Mr. Sedgwick. It gave an account 

 of the development of the marsupial embryo, which has been 

 hitherto a riddle in biology. A letter from Mr. Caldwell as to 

 the progress of his investigations in Australia was also read. 



On Some Peculiariies in the Geographical Distribution and 

 Habits of Certain Mammals Inhabiting Continental aad Oeeanic 

 Islands, by G. F.. Dobson, M.A., F.R.S. — The geographical 

 distribution of mammals inhabiting continental and oceanic 

 islands has been lately so ably treated of by Mr. Wallace, in his 

 work " Island Life," that I do not purpose entering upon the 

 subject from a general point of view, but will limit my remarks 

 to some peculiarities of distribution which have attracted my 

 attention while engaged in the special study of certain mam- 

 malian orders : I refer particularly to the Chiroptera and Insecti- 

 vora. It is an interesting fact, not hitherto noticed, that many 

 of the most characteristic species of the Chiropterous fauna of 

 Australia have their nearest allies, not in the Oriental, but in the 

 Ethiopian Region, thus contrasting remarkably with the avifauna. 

 The remarkable genus Chahnolobus is represented only in Africa 

 south of the equator and in Australia, a single species extend- 

 ing into New Zealand. Again, the species of the -ub-genus 

 Mormoptems, which belongs to a genus (Nyctinomus) of world- 

 wide distribution, is limited to the same zoological regions, being 

 found only in Africa south of the equator, Madagascar, the 

 Mascarene Islands, Australia, and Norfolk Island. The presence 

 of a species of this genus in Norfolk Island and its absence from 

 New Zealand is very remarkable, for, as I pointed out for the 

 first time about ten years ago, one of the two New Zealand bats 

 known, namely Ckalinolobits tubereulatus, is also common in 

 Australia. The species of the exh aordinarily specialised genus 

 Megaderma have their headquarters in the Oriental and Ethio- 

 pian Regions ; yet the largest species not only of the genus, but 

 also of all known insectivorous bats, namely M. gigas, lately 

 described by the writer from Central Queensland, has its nearest 

 ally, not in any of the Oriental species, but in M. cor from 

 Eastern Africa. Another very remarkable leaf-nosed bat, the 

 type of my genus Triaznops, found in Madagascar, Eastern 

 Africa, and Persia, but unknown in the well-searched Oriental 

 Region, has its nearest and only ally in Rhinonycleris aurantia of 

 Australia, the type of another very peculiar genus. Finally, 

 Australia agrees much more closely with Madagascar and the 

 Mascarene Islands than with the Oriental Region in the species 

 of the large genus Pleropus, for, while species of the section of 

 which Pi. vulgaris of Madagascar is characteristic are well re- 

 presented in the former regions, they are absent from the latter. 

 Furthermore it is noticeable that, while So per cent, of the 

 species of the genus inhabit the Australian Region and Mada- 

 gascar with its islands, a single species only has found its way to 

 the great continent of Hindostan and to Ceylon. 



On the Geographical Distribution of the T.arida (Gulls and 

 Terns) with Special Reference to Canadian Species, by Howard 

 Saunders. 



Res 'ilt of the Investigations of Insular Floras, by \V. B. 

 Hemsley. 



Some Observations on the Direct Descendants of Bos pri mi- 

 genius in Great Britain, by G. P. Hughes. 



On Natural Co-ordiua'ion as Evinced in Organic Evolution, 

 by Dr. W. Fraser. 



Department of Anatomy and Physiology 

 On the Pr sence of Eyes and Other Sense- Organs in the Shells i 

 of Chitonida, by H. N. Moseley, M.A., F. R. S., Linacre | 

 Profes-or of Human and Comparative Anatomy in the Uni- 



versity of Oxford. — The Chitonidoe have hitherto been regarded 

 as characterised by an entire absence of organs of vision, the 

 presence of eyes in the shells of numerous genera having been 

 entirely overlooked by naturalists. The author first discovered 

 eyes in a specimen of Sehizochiton incisus, dred/ed by Capt. 

 Chimmo, R.N., in the Sulu Sea, in which species they are 

 larger and more conspicuous than elsewhere, and on examining 

 carefully the shells of certain other forms, found eyes present 

 there also. 'Die eves are entirely confined to the shells, and to 

 thi I 1 -nils of these, the "tegmenta" not occurrins; at all 



on the " articulamenta." They never occur on the girdle or 

 z:me, or any other part of the mantle. They appear as bright, 

 highly-refracting, convex beads on the shell-surfaces, encircled by 

 zones of dark pigment formed by the choroid layers. The eyes 

 are usually circular in outline, and very minute, measuring in 

 Schtzochiton incisus about l/i75th of an inch in diameter, in 

 Acanthopleura spiniger l/35oth of an inch, and in Ccrphieum 

 aculeatum, in which thev are oval in outline, i/6ooth of an inch 

 by all nit 1 400th. In the case of all the intermediate shells the 

 eyes are confined to the ares laterales, or to the lines of demar- 

 cation between the areae laterales and the area centralis, which 

 latter is usually entirely devoid of them. In some genera of 

 Chitonidaj, such as Acanthopleura and Corephicum, the eyes 

 appear to be often destroyed and obliterated in the older regions 

 of the shells by decay and delamination of the tegmental surface, 

 or its destruction by boring Algae or animals. They are, how- 

 ever, constantly re-formed by the mantle in the process of 

 growth of the shell at the growing margin of the tegmentum, 

 and may be observed in this situation in all stages of construc- 

 tion. In other genera, such as Tonicia, the eyes lie in shallow 

 pits of the shell-surfaces, and thus escape destruction by wear, 

 nearly the entire number which have been f irmed being thus 

 found present in fully-grown shells. The tubercles and pro- 

 minences by which the tegments are covered in some forms 

 serve, perhaps, as protections to the eyes from attrition. The 

 entire substance of the tegmentum in the Chitonidfe is traversed 

 by a series of branching canals, which are occupied in the living 

 animal by corresponding ramifications of soft tissue and nerves. 

 The strands of soft tissue are continuous with the tissues 

 of the mantle along the line of junction of the margin of the 

 tegmentum with the upper surface of the articulamentum by 

 means of a series of tubular perforations in the shell-substance. 

 Further, in the intermediate shells of most genera there are a 

 pair of lateral slits (incisurae laterales), one on either side in each 

 shell in the lateral laminae of insertion ; these slits lead each to 

 a narrow tract in the deep substance of the shell, which follows 

 the line of separation between the area centralis and area 

 lateralis. This tract is permeated by longitudinal canals, into 

 which open a series of five apertures on the under surface of the 

 shell. By these apertures numerous nerves enter the tract from 

 the bed of the shell, and, traversing the longitudinal canals, give 

 off a serie; of lateral branches on either side from it to the net- 

 work within the tegmentum. In the cases of the anterior and 

 posterior shells, there are -usually a considerable number of 

 slits present in the laminae of insertion, each connected with a 

 similar nerve-supply to the tegmentum. The network terminates 

 at the surface of the tegmentum all over in a series of elongate 

 cylindrical organs of touch, the pluj-like ends of which are 

 somewhat dice-box shaped, and can be protruded beyond the 

 level of the tegmental surface from a series of pores, "macro- 

 pores," by which this surface is covered. These 1 irger organs 

 of touch give off from their sides five branches of soft tissue, 

 which pass vertically to the surface of the tegmentum, and ter- 

 minate tlvre in minute p'ug-like organs like the larger ones, 

 but much smaller, and which are protrusible from a serie- of 

 smaller pores (micropores) in the shell-substance. These smaller 

 and larger touch-organs, and their corresp nding pores, are dis- 

 posed on the surface of the tegmentum with more or less exact 

 regularity in different genera of Chitonidae ; in many cases in very 

 definite lines and patterns. The eyes are connected with the 

 same network of soft tissue as the touch-organs, and are appa- 

 rently to be regarded as having arisen in development as special 

 modifications of them. The soft structures of each eye lie in a 

 more or les< pear-shaped chamber excavated in the substance 

 of the tegmentum. The stalk of the pear, which forms the 

 canal for the passage of the ootic nerve, is directed always 

 towards the free margin of the tegmentum, and here its wall 

 is pierced by a circular aperture, which is c .vered by the c irnea. 

 The cornea is calcareous, resisting the action of strong b liling 

 caustic alkalis, but co'lapsing at once when treated with acid . 



