During recent years there has been a very great advance in our knowledge of the minute structure and function of the various regions and glands of the alimentary canal of the prosobranch and pulmonate gastropods, without any corresponding increase in our understanding of the opisthobranch and, in particular, of the nudibranch gut. That the emphasis should be laid on the streptoneurous and the land-living forms is obviously due to their abundance and to the fact that they include almost all the familiar types of gastropod mollusc, but it is disappointing that, at the moment of writing, there exists only one account of the histology and function of the digestive system of either a dorid or an æolid—to confine attention to the two main types of nudibranch molluscs which occur in British waters—that of Millott (1937b). This is perhaps more noticeable when it is recalled that the nudibranchs have specialised along distinctly unusual lines, many of which are intimately associated with the food and feeding habits which the animals have adopted. The æolids, it is true, have attracted a lively interest in connexion with their possession of nematocysts, but the majority of investigators have apparently been content to trace these into the cnidosacs without concerning themselves over the other constituents of the animal's food.

In 1790 Goethe (Eng. Trans., 1863) published his doctrine of metamorphosis. Before that only two authors had expressed any fundamental ideas with regard to the flower. Wolff in his Theoria Generationis (1759) said that the plant consisted of nothing but stem and leaf, the root being a modification of the former; parts of the flower were appendages, and the production of floral leaves was due to degeneration of the sap, the richest portion being used up at a lower level by the vigorous first-formed foliage leaves.

Linné (1760) expressed the same idea as Wolff, partly basing his evidence on teratological specimens, in which the various floral organs were sometimes found to be replaced by leaves. He further considered the flower to be a modified shoot, five years' growth being compressed into a single year. Believing that the different floral whorls were developed the one from the other, and observing that they encircled each other, he attributed the various floral envelopes to different tissues of the stem—e.g. the bark gave rise to the calyx, and the carpels arose from the pith.

In recent years intensive investigations on the plumage dimorphism characteristically developed in most breeds of domestic fowl have resulted in a great increase in our knowledge concerning the rôle of the endocrine glands, in particular the thyroid and sex organs, in relation to plumage differences. Since, however, the majority of these researches have been directed to the plumage exhibited by the adult bird, it is suggested that an analysis, both observational and experimental, of the earlier plumage phases shown successively from hatching to maturity might yield much valuable data concerning the nature of the hormonic stimuli involved.

The publication by Kidston and Gwynne-Vaughan ïn 1912 of a memoir on Stenomyelon tuedianum Kidston marked the beginning of a proposed series, which was never continued by them, on the Carboniferous Flora of Berwickshire, based upon material collected during 1900 and 1901 from rocks of the Calciferous Sandstone Series (Cementstone Group) at various localities in Berwickshire while Kidston was working with Mr A. Macconochie of the Geological Survey. Brief notes on this material, with identifications of some of the plants found in compression form, were contributed by Kidston to the “Summary of the Progress of the Geological Survey” (Kidston, 1901, 1902 a), where he commented upon the interest and importance of the material; but beyond recording the occurrence of petrified specimens, no further description of these was given at the time. An incomplete list of anatomical species identified from this Berwickshire material was also given by Kidston at a later date (Kidston, 1923, p. 19). Some of the petrifactions, in addition to the Stenomyelon tuedianum already referred to (Kidston and Gwynne-Vaughan, loc. cit.), have been described by various writers, mostly from specimens in the Kidston Collection of Fossil Plant Slides in the Botany Department of Glasgow University, where the majority of the sections is to be found.

Among Gasteropod Molluscs the life-histories and development of the most highly evolved members, the terrestrial Pulmonates, have been less intensively studied than those of more primitive aquatic forms. This has been due in part to the technical difficulties involved in the permanent preparation of material for study, and in part to the fact that the investigator seeking for primitive features of phyletic interest is more likely to find these among more generalised species of Gasteropods than among those which are obviously adapted, both during the early stages of their development and in adult life, to a habitat far removed from the ancestral one.

It is the purpose of this paper to present data bearing upon the life-history of a single species of land Pulmonate, Agriolimax agrestis L., to enlarge upon certain aspects of the embryology of this species, and to demonstrate the structural and functional changes of the larva which have accompanied the transition from an aquatic to a terrestrial breeding habit.

The present work on Apseudes talpa forms the second and concluding part of an investigation undertaken in an attempt to discover from feeding mechanisms the steps by which the higher Peracarida may have been derived from a primitive Mysid-like ancestor. The first part of the work consisted of an account of the feeding mechanism of Diastylis bradyi (Dennell, 1934), but it was felt at that time that a discussion of its significance could usefully be postponed until the completion of the work on Apseudes. It is now possible, in view of the accounts of feeding in Hemimysis (Cannon and Manton, 1927), and in Gnathophausia and Lophogaster (Manton, 1928), to discuss with some measure of completeness the feeding mechanism of the Peracarida.

Owing to the comparatively rare occurrence of most tectibranchs it is perhaps not surprising to find that, in spite of the ever-increasing knowledge of the histological structure and functioning of the alimentary canal of molluscs, little attention has been paid in this respect to these forms. The structure of the radula and gizzard has previously aroused interest, but so far as the rest of the alimentary canal is concerned most workers have been content with a somewhat superficial description of the gross morphology such as was given by Vayssière (1880), Bouvier (1893), Pelseneer (1893, 1894), and Guiart (1901). A more recent account of the digestive tract of Philine aperta has been given by Brown (1934), but this includes no histological or physiological consideration.

Our district (Pl. II) includes an exceptionally beautiful tract of the Highlands, stretching from the Errochty Water, half a dozen miles north-east of Kinloch Rannoch, to near Loch Tay. It reaches its greatest height in Beinn a' Chuallaich (2925 ft.), Schiehallion (3547 ft.), Carn Mairg (3419 ft.), and Carn Gorm (CG, Pl. II, 3370 ft.). These, with companion mountains that closely approach the 3000-foot contour, are remnants of the much dissected Highland plateau. There are two main eastwardly-draining valley systems: the more northerly holds Loch Rannoch and the River Tummel; the more southerly is known throughout its length as Glen Lyon. The southern limit of the district approximately follows the divide between Glen Lyon and Loch Tay, but fails to include the summit of Ben Lawers (3984 ft.) (inset, text-fig. 14). The eastern margin is really marked by the great Loch Tay fault; though, for purposes of comparison, some previously published mapping is reproduced on PL II east of this fault. The Tummel and the Lyon cross the Loch Tay fault at about 450 and 400 ft. above sea-level.

The following account deals with investigations pursued by the authors during the years 1931 and 1932. Pressure of other and later work precluded the possibility of the results of the investigations being published until this year. It is believed that no recent account of the cuticular-scale pattern of monotreme hairs has been published, and the authors are convinced of the desirability of such a detailed description. When this work was commenced it was intended to be the first of a series of investigations into the scale- pattern of mammalian hairs. Hitherto work in this direction has only taken the form of either a consideration of one species only, or generalisations upon the scale-pattern of a group of mammals. Such generalisations would appear to be often unjustified for the following reasons: In many instances they are based first upon an insufficient number of observations along the length of each fibre, and secondly upon a technique of preparing the fibres for examination which would seem to be inadequate for accurate vision of all the delicate lines marking the boundaries of the scales. Although notable attempts to indicate these boundaries have been made (Hausman, 1920; Glaister, 1931), in the authors' opinion the results have not been satisfactory. Moreover, until Manby's methods, described in previous papers and also in this account, were perfected, there has been no really satisfactory method of photographing cuticular-scale patterns accurately.

Following the discovery of well-preserved fossil plants at Weak Law, North Berwick (Gordon, 1935, p. 280), a search of all the volcanic ashes in the neighbourhood was undertaken and special attention was given to those localities from which plant-remains had been recorded in the past. Isolated specimens had been from time to time discovered, but were usually of an unsatisfactory character—mostly fragments of charred wood such as frequently occur in volcanic ashes. More satisfactory specimens were found by Mr James Whitecross of North Berwick, and were recorded by the late Mr T. Cuthbert Day (Day, 1928, p. 48), from a thin bed of limestone in the ashes of Gin Head, Tantallon, and elsewhere in the vicinity.

Since the preliminary cytological work of Doncaster (1906) nothing has been recorded on the maturation of the thelytokously (female-producing) parthenogenetic saw-flies (Ten-thredinidæ). Doncaster worked with the four species now known, according to Enslin (1918), as Empria abdominalis F., E. pulverata Ritz., crœsus varus Vill., and Hemichroa crocea Geoffr., and he concluded (1907) that the chromosome number in the oocyte, polar nuclei and egg pronucleus was 8, there being two maturation divisions giving rise to an egg pronucleus and three polar nuclei. As stated in our note to Nature (1937) recent work on the thelytokously parthenogenetic species, Pristiphora pallipes Lep., by our colleague, Mr L. C. Comrie, confirms Doncaster regarding the number of maturation divisions and polar nuclei, but raises strong doubts on Doncaster's interpretations of chromosome number and behaviour. Doncaster did not make it clear whether the diploid number was 8 or 16, or whether auto regulation occurred during or after maturation. It appears probable that the real diploid number is 16, for intensive study of over twenty species of saw-flies, carried on mainly by Dr F. Greenshields in this department (unpublished work), shows that the characteristic diploid number for Tenthredinidæ is 16. Further, judging by Mr Comrie's research on Pristiphora pallipes, in which the diploid number is also found to be 16, it would appear probable that autoregulation in Doncaster's types is brought about by fusion of egg pronucleus and second polar nucleus.

The work described in this paper was carried out in the Department of Zoology of Birkbeck College, University of London, and at the Marine Laboratories at Plymouth and Port Erin. I wish to acknowledge my indebtedness to the University of London for the use of their table at Plymouth, to Birkbeck College for a grant of £5 towards the illustrations, and, in particular, I would express my gratitude to Mr Graham, under whose direction the work was carried out, for his continued kindness and help.

The specimens of Lepidochitona cinereus which were used for the investigation were collected at Bangor, Plymouth and Port Erin, and also obtained from Cullercoats. Most of the material from Plymouth and one specimen from Cullercoats was infected with the Haplosporidian parasite Haplosporidium chitonis (Debaisieux, 1920) and was therefore unreliable for histological and physiological work. Specimens of Acanthochitona crinitus were collected at Plymouth, and showed no sign of infection with Haplosporidium chitonis; a few, however, were slightly parasitised with another Sporozoan. The Californian species Ischnochiton magdalenensis and Cryptochiton stelleri were obtained from Turtox General Biological Supply House, Chicago. Specimens of these species were fixed in formalin, which proved to be a poor fixative for histological work.

In a former memoir (1934) the author described the early development of the ferret from fertilisation to the formation of the prochordal plate. The following is a continuation of that work and describes the development of the mesoblast and notochord from their incipient phases to a stage with seven somites when the definitive notochord begins to separate from the notochordal plate. As far as can be ascertained these phases have not been previously described in the case of the ferret, although the literature on gastrulation and the formation of the notochord and mesoblast is voluminous. A résumé of the descriptions and theories of gastrulation has already been fully summarised by Rabl (1915), and later by Van Oordt (1921). Opinions concerning notochord and mesoblast formation will be referred to in the following pages, and as there is great confusion of nomenclature in it I have appended a Glossary of the terms which I have used and the meanings that I attach to them (p. 188).

La Scotia a recueilli, dans les régions antarctiques, un petit nombre de Crïnoides; mais cette collection, quoique restreinte, est intéressante et je regrette vivement que diverses circonstances, indépendantes de ma bonne volonté, ne m'aient pas permis d'en faire une étude complète.

Parmi les formes libres se trouvent des exemplaires se rapportant à l'Isometra vivipara Mortensen, espèce incubatrice présentant, dans des pinnules élargies à leur base, des œufs en voie de développement et dont quelques cirres portent des larves au stade pentacrine. Ces exemplaires ont été recueillis au “Burdwood Bank,” comme ceux dont Anderson (1904) avait décrit le mode d'incubation sous l'appellation d'Antedon hirsuta Carpenter et qu'Austin Clark (1915, p. 146) présumait devoir être Isometra angustipinna (Carpenter) ou une forme voisine. Mais Mortensen (1918, p. 10) examinant les échantillons rapportés par l'Expédition antarctique suédoise de cette espèce incubatrice la considére comme nouvelle et la décrit sous le nom d'Isometra vivipara.

The study of differential fertility in Great Britain in relation to the continued decline in fertility has been hampered by lack of adequate birth registration. Though the defect has now been partially remedied by The Population (Statistics) Bill, the study of past changes is still difficult. In a previous memoir (Charles and Moshinsky, 1938) the writer gave an analysis of regional fertility differences in England and Wales from 1911 to 1931. Gross reproduction rates were used as measures of fertility. In the present communication the same method is applied to changes in fertility in Scotland.

Descriptions of the two Coal Measure plants Senftenbergia and Dactylotheca have appeared in the literature on numerous occasions previous to this account. The former genus was first described by Corda (1845), and the latter by Zeiller (1883). Other contributions have been made by more recent investigators, and these have since been revised and supplemented by Kidston (1924). In each case the account was based upon an examination of the material as it appeared on the rock in the form of a compression. More recently, however, newer methods for dealing with plant compressions have been devised, and it was felt that the application of an improved technique would furnish a more adequate description of the plants, particularly of their fruiting members.

In a previous communication (Charles, 1938) gross reproduction rates were given for the counties, cities and burghs, and for the urban and landward areas of Scotland. The present communication is an attempt to correlate differences among these rates with measurable social circumstances, more especially with occupation and with frequency of marriage. Attention will be directed mainly to such differences in 1931.

In my account (Read, 1935) of the metamorphic geology of Unst, in the Shetlands, I have shown that the island is made up of a series of tectonic units separated from one another by dislocations of various kinds. The rocks of most of the units have lengthy metamorphic histories that are different in the different units.

This present communication deals with one tectonic unit, the Valla Field Block. The metamorphic history of this block can be divided into three stages, each characterized by the type of pressure-temperature factors operative during it. It is my main purpose here first to give the evidence, derived from the study of the pelitic rocks, on which this subdivision is based, and then to examine the behaviour of the various other rock-types during the three episodes. The results show that the stability of certain minerals depends upon the bulk-composition of the rocks containing them. In polymetamorphism of the Unst type, the minerals cannot be considered apart from the rocks in which they occur—a point of importance for Highland geology in general.

During five seasons the writer has been investigating the fishes of the Middle Devonian flagstones in the quarry at Achanarras in Caithness. This celebrated quarry, the home of Palœospondylus, has been long known and has been previously worked by Traquair (1890, 1894), who has described its fauna. There appeared, however, still to be room for a more detailed and intensive examination of the fauna such as could only be produced by a more extended period of work than had so far been given to it. By permission of Colonel Murray-Thriepland, the owner of the estate on which the quarry is situated, I have been able to spend the seasons of 1931–1935 in making a collection, of which a part is now to be described. To the Colonel and to his son Mr Peter Murray-Thriepland I have been indebted throughout for their unfailing interest and assistance. The main part of this account was written in 1934, but was not published owing to the discontinuance of a foreign journal for which it had been accepted. The season of 1935 produced some further material, which has now been incorporated. Meanwhile the writer has had the opportunity of discussing questions relating to the genus Dipterus with Dr Stanley Westoll, who has in preparation a work on the Devonian fishes in general, and is indebted to him for information on several points. Dr Westoll's view that the scales show an alternate deposition and resorbtion of the outer layer together with its bearing on questions of species is here fully adopted (Westoll, 1935).

In 1858 C. H. Pander described as Ptydodus a number of teeth from Upper Devonian limestones in Russia. His admirable figures of complete teeth and of sections through them established the very chimæroid structure of these bodies. Since that time similar teeth have been repeatedly described, and have served for the establishment of three genera and many species from rocks of Middle and Upper Devonian age.