Gymnadenia conopsea and albida differ in detail only from Orchis. Habenaria chlorantha has a drum-like viscid disc of great functional importance, but its structure and action are far too complicated to be abridged here. H. bifolia is found to differ in so many characters from H. chlorantha as to be considered an undoubtedly good species, and further it is fertilized in a totally different manner. Epipactis palustris. The labellum is of peculiar structure, the distal half being hinged on the other so lightly that a fly depresses it. An insect entering the flower depresses the distal portion (which closes after it), and reaches the nectarial cavity without touching the rostellum; but, in backing out, the action of raising the said distal portion forces the insect against the rostellum, when it removes the pollen. There is no movement of depression required; for, on the entrance of the insect in another flower, the pollinia it bears are brought into immediate contact with its stigmatic surface. In E. latifolia, the distal portion of the lip is not flexible, and the operation is more simple. Cephalanthera grandiflora presents the all but unique case of an Orchid wanting the rostellum (Cypripedium being the only other); its pollen grains are separate and spherical. Here perpetual selffertilization is imperfectly secured by the friable pollen grains reaching the stigma at a very early period indeed; but the structure of the flower and relations of the parts are such that insects must help, so that the flowers are partially fertilized by their own pollen and partly by that of other flowers. The details are very intricate, and the discussion highly interesting and curious. Goodyera repens is one of the most interesting British Orchids, as connecting several distinct forms; in the development of a caudicle and cohesion of the pollen grains, it approaches the tribe Ophrea; in other respects it is allied to Epipactis, Spiranthes, and Orchis. Spiranthes autumnalis. The rostellum here bears an erect boatshaped disc, filled with a viscid fluid, and decked with a membrane endowed with the power of fissuring on the slightest stimulus (but not spontaneously). The pollinia consist each of two brittle, leaflike faminæ, and are exposed by a contraction of the anther case. The lip, at an early period, moves away from the rostellum, leaving a narrow passage to the nectary. The flowers are visited by bees, which touch the rostellum with their proboscis, causing the boat's deck to burst and expose the viscid fluid which attaches the pollinia to their proboscis. But at the period when the flower is open enough to allow of bees removing the pollinia, the aperture is not sufficiently wide to allow this to be applied to the stigma. The flower thereafter opens wider by the further movement of the labellum; hence it happens that fully expanded flowers are fertilized by newly expanded ones. The analysis of the whole operation is most graphically given by Mr. Darwin. Malaxis paludosa has flowers with the lip turned upwards, owing to a greater than usual twist of the ovary, and the upper sepal and petal are reflexed instead of protecting the flower. The pollenmasses are almost wholly exposed, and so placed that an insect must withdraw them on visiting the flower, and carry them off lying parallel to its proboscis, and in the proper position for being applied to the stigmatic cavity of the next flower visited. Listera ovata. The rostellum is here exceedingly curious, being divided internally into loculi, a structure found in no other Orchid but Neottia. It is exquisitely sensitive, rupturing suddenly with a touch of the finest human hair, and ejecting a ball of viscid matter at its apex. The pollinia, which lie free and are very friable, have their bases so close to the apex of the rostellum, as to be invariably entangled in the expelled viscid mass. The long lip presents a longitudinal nectarial ridge. Insects visit this, crawl upwards, touch the apex of the rostellum, when the viscid matter shoots out, carrying the pollen masses by their entangled lower ends, and glueing them to the insect's head The insect visits other flowers, and masses of the friable pollen are left on their stigmatic surfaces. Listera cordata and Neottia nidus-avis present essentially the same structure and method of fertilization as L. ovata. To complete this extremely brief and incomplete account of the phenomena in British Orchids we should by right allude to Cypripedium, of which genus however only exotic species were examined. This genus, as is well known, differs from all other Orchids in having three confluent stigmata (hence no rostellum), the anther of other Orchids represented by a shield-like body, two fertile anthers, and in the pollen grains being glutinous. Fertilization seems here to take place by insects visiting the flower to extract the sweet fluid from the glandular hairs within the labellum; to effect this they insert their proboscis into a narrow chink which leads to the anthers, the sticky grains of which attach themselves to their proboscis, and are conveyed to other flowers. Cypripedium is thus the only genus in which the pollen grains attach themselves not only to the insect's proboscis but to the stigmatic surface, which is not viscid. We have preferred thus giving a rather extended resumé of Mr. Darwin's observations on British Orchids to reviewing the very extensive and intricate chapters devoted to foreign Orchids, the homologies of Orchid flowers, and general considerations; both because they may be repeated by any observer and extended by many, and because this procedure of ours gives a better idea of the completeness of the work than a more sporadic selection of his observations and experiments, results and conclusions, could have. Those other chapters are however by far the more interesting and important, and to them we shall at some future time recur, if opportunity offer. It remains to add that the work is copiously illustrated with most useful and in general very clear woodcuts, which would, however, have been greatly increased in value had the insects been introduced, in position, on the flowers. 377 Original Articles. XXXVI.-A REPORT ON RECENT RESEARCHES INTO THE MINUTE ANATOMY OF THE SPINAL CORD. By W. B. Kesteven, F.R.C.S. [With Plates IX. X. XI.] THE object of the writer has been to collect in brief compass, from various essays and monographs, the principal results of recent researches into the microscopic anatomy of the spinal cord, embracing, on the present occasion, that portion only of the cord which extends from below the medulla oblongata. The several essays by Mr. Lockhart Clarke have been followed as the basis of the following remarks, and the information is conveyed for the most part as nearly as possible in the words of Mr. Clarke. Lest it should appear that an undue prominence is thus given to the observations of that anatomist, it should be borne in mind that the advances recently made towards an accurate insight into the relations of the elements of nervous structures, are mainly due to the method of preparing transparent sections, which was introduced by Mr. Clarke, and which with some slight modifications has been followed by subsequent investigators, who have all more or less confirmed the accuracy of his observations. Stilling's magnificent and voluminous treatises having been founded upon the results of the examination by reflected light, of thin sections of simply hardened cord, afforded conclusions which have been shown by later observers to be in many points obscure and erroneous. The great diversity of opinion that, until very lately, existed on almost every point of the anatomy of the nervous centres, may be learnt from the historical sections of Schroeder van der Kolk's, Stilling's, and other essays-while a notable. approach towards agreement in observations and inferences, has been perceptible since the examination of transparent sections by means of transmitted light. The following Bibliography embraces all essays or works having reference to the microscopic anatomy of the spinal cord, of which the writer has been able to avail himself. It is from no want of appreciation of the value of the labours of Grainger, Solly, Bowman, Todd, and other previous anatomists, that this subject has been taken up at a late point in its history. To have done otherwise would have been to occupy the pages of this journal with an historical disquisition foreign to its objects and superfluous to its readers. J. LOCKHART CLARKE.-1. Researches into the Structure of the Spinal Chord. Philosophical Transactions, 1851.-2. On certain Functions of the Spinal Chord, with further investigations into its Structure. Philosophical Transactions, 1853.-3. Further Researches on the Grey Substance of the Spinal Chord. Philosophical Transactions, 1859. B. STILLING.-1. Neue Untersuchungen über den Bau des Rückenmarks. Fünf Lieferungen, Frankfurt, 1856-1859.-2. Atlas Mikroskopisch-Anatomischer Abbildungen. Vier Lieferungen, KÖLLIKER.-Manual of Human Histology. London (Sydenham Society), 1853. 1856-1859. PH. OWSJANNIKOW. - Disquisitiones Microscopica de Medulla FR. GOLL.-Denkschriften der Mediz.-Chir. Gesellschaft d. Kanton J. B. TRASK.-Contributions to the Anatomy of the Spinal Cord. San Francisco, 1860. E. REISSNER.-Beiträge zur Kentniss von Bau des Rückenmarkes von Petromyson fluviatilis. Dorpat. 1860. L. STIEDA.-Ueber das Rückenmark und Einzelne Theile des Gehirns von Esox Lucius. Dorpat. 1861. J. DEAN.-Microscopic Anatomy of the Lumbar Enlargement of the Spinal Cord. Cambridge, U.S. 1861. J. TRAUGOTT.-Contribution à l'Anatomie Microscopique de la moëlle epinière de la Grenouille. Quoted from the German, in Brown-Séquard's Journal de Physiologie, Janvier, 1862. The subject will be treated under the three heads of: 1. The structure of the white columns. 2. The form and structure of the grey matter. I. STRUCTURE OF THE WHITE COLUMNS. -- The anatomical elements of the white columns present different appearances, according as they are examined in longitudinal or in transverse sections. A longitudinal section exhibits the general aspect of a structure consisting of parallel fibres running lengthwise. A minute examination shows them, as described by Mr. Lockhart Clarke, to consist of nerve-fibres taking different directions,-transversely, obliquely, and longitudinally, together with blood-vessels and connective tissue. On tracing the transverse fibres, these are found to proceed from the grey matter, or from the nerve-roots, and to form a kind of plexus between bundles of the longitudinal fibres, with many of which they may also be seen to become continuous after altering their course. A large number of these transverse fibres approach the surface in fissures which contain connective tissue, and admit the passage of vessels from the pia mater of the surface. Within the grey substance they may be traced in connection with the roots of nerves, with the processes of the multipolar cells, and with the fibres which form the commissures. The oblique fibres may be regarded as intermediate between the transverse and the longitudinal; they form the deeper strata of the cord, lying nearer to the grey matter from which they proceed upwards and downwards, becoming longitudinal after running a variable distance. The longitudinal fibres constitute the greater portion of the mass of the white columns; they are the more superficial, and run nearly parallel to each other. Dean describes four principal courses of the longitudinal fibres :1st, obliquely upwards and inwards, penetrating sooner or later into the grey substance: 2nd, fibres which may be slightly oblique at starting, but soon assume a directly transverse course, sometimes varying this by slightly ascending or descending; these fibres are mostly of the finest sort : 3rd, fibres which enter the posterior column at various angles, but very soon bend round, often at quite a sharp angle, descending in a course more or less oblique: 4th, fibres which are looped or recurrent, seeming to unite both ascending and descending fibres. Besides these four classes, the first three of which have already been noticed by Stilling, Dean observes, "every variety of intermediate course will be found, the bundles of fibres being braided together in most complex manner.' "The anterior and lateral columns, apart from the anterior roots, are only partially derived from the cells of the anterior and posterior cornua, some of the white longitudinal fibres seeming to be direct continuations of the posterior roots, after these have passed through the grey substance; the posterior columns are composed almost exclusively of the posterior roots, a few fibres appearing to be derived from cell processes coming from the large cells, situated on the margin of the posterior cornu: what course these fibres take after leaving the grey substance, I have been unable to determine definitely."-p. 10. Stilling also points out that the longitudinal fibres do not all follow a parallel course, but that many, after a longer or shorter extent, bend in other directions; but whether all or only some are thus diverted, and whether others continue to follow the whole length of the cord, he has not determined. Sometimes horizontal fibres are traceable into the roots of the nerves. The oblique fibres he describes, similarly with Mr. Lockhart Clarke, as passing upwards and downwards, and in one of his plates gives an illustration of their crossing one another. The transverse fibres, Stilling remarks, are more numerous where the larger nerve roots arise. Their course is not always in exactly the same plane, neither are they always straight, but present N. H. R.-1862. 2 D |