The present paper is the second of a series of investigations into the anatomy of the lower Dicotyledons (1), aiming at the accumulation of anatomical data which, it is hoped, may prove of service in elucidating the phylogeny of the complex of orders usually regarded as situated somewhere near the base of the Angiosperm phylum. The continuance of the War has again materially retarded these investigations, and has also rendered it almost impossible to obtain material from abroad that would, doubtless, have been available in peace time. We are greatly indebted for substantial assistance in this relation more especially to Sir David Prain, F.R.S., Director of the Royal Botanic Gardens, Kew, and to Sir Frederick Moore, F.R.S., Director of the Glasnevin Gardens, Dublin, and to them we tender our grateful thanks.

In a general survey of the pinna-traces of Ferns (Davie, '14), the results of which have been summarised in tabular form (loc. cit., p. 354), two main types of pinnatrace were described and contrasted. In the one—the “extramarginal”—the pinnatrace leaves the back of the hook formed by the incurved edge of the leaf-trace; in the other—the “marginal”—the outwardly directed margin of the leaf-trace is simply nipped off as the pinna-trace. The more primitive Ferns in the evolutionary scale, and the first leaves of both primitive and advanced Ferns, exhibit the marginal type of pinna-trace; the extramarginal type of pinna-trace is found in those Ferns which stand midway between the extreme types in the system of classification, and in some advanced forms.

From a biological point of view considerable interest must always attend any investigation of the earliest known organisms, and, although we may legitimately infer that a flora and fauna existed prior to Cambrian times, the organisms preserved for us in rocks of that age constitute, at present, the first chapter of palæontological history. For this reason alone the Archæocyathinæ are important, since they form part of the Lower Cambrian fauna. When, however, we consider that the genera included in the group are very distinct from one another (indicating that the family was probably of considerable antiquity even in those early times), that the types have, as far as we know, a wide geographical distribution, and that to certain skeletal characters usually associated with the Porifera they unite others more common among the Cœlenterata, interest is still further stimulated. On the other hand, although recorded in great abundance from several widely separated localities, they are not, as a rule, common fossils in Cambrian strata, and consequently the group has not received much attention.

Examination of living embryos has shown that the heart is a functionally active organ from a very early stage of its development. At all periods of life the result of the functional activity is in essentials the same, viz. the propulsion of the blood in a definite direction through the heart into the vessels arising from it; but the mechanism for effecting this propulsion undergoes profound alterations, and the heart becomes transformed from a simple continuous tube, destitute of valves, whose walls contract in a rhythmic peristaltic wave, into a complex four-chambered organ, divided into right and left portions, which are ultimately completely separated from one another, possessing valves, and contracting not in a peristaltic wave but in alternating consecutive contractions of the atria and ventricles of the right and left sides simultaneously. Coincidently with the changes in the heart itself, profound alterations occur in the vessels leading to and from the heart. In this combination of simultaneous development and functional activity the heart differs from the other organs of the body, and hence its development presents special problems involving the function as well as the structure of the different parts. Our knowledge of the development of the heart in man cannot yet be said to be complete.

The present paper is the third of a series of researches on the anatomy of the lower Dicotyledons undertaken with the object of seeing what, if any, aid anatomy might give in determining the point of origin of the so-called Monocotyledons. It deals more especially with the anatomical and histological peculiarities of the stem of the Calycanthaceæ.

A few words of explanation are necessary at the outset in connection with the terms used in association with the animals upon which these investigations were made.

Dealers in ferrets supply two types of animals—one with yellowish-white fur and pink eyes, which they call “ferrets,” and a second type in which the yellowish fur is intermingled with a varying admixture of brownish or brown-black hairs; the second type they call “polecats.” The polecats of the ferret-dealers are not, however, true polecats, for Miss Frances Pitt, who has bred ferrets and polecats and ferret-polecat hybrids in a scientific manner, and to whom I am indebted for the greater and best part of my information on this subject, points out that the so-called polecat of the dealers is never so dark and handsome in colour as the true polecat. Moreover, as Miss Pitt states, in the true polecat the light marks in front of the ears do not usually join across the forehead, whereas in the polecat of the dealers they form a band across the face; further, when viewed from in front and above, the head of the true polecat has the form of a fairly equilateral triangle, whilst in ferrets and the so-called polecats of the dealers the head, on the whole, has the form of an isosceles triangle.

That there is a decided need for the ecological study of insects and other animals was first brought home to the mind of the author whilst engaged upon the subject of a “General Survey of the Insect Fauna of the Soil” (vide Jour. Econ. Biol., vol. viii, part 3, 1913). Much information has been collected at various times by numerous authors, and especially those who have treated of the habits and behaviour of animals, but very little attempt has been made to systematise the data variously gathered, to explain the cause and effect of many obscure phenomena, or to make important observations accessible for the use of the animal ecologist. Thus, at present, we find ourselves on the threshold of practically a new and undisputed field, with opportunities for original and interesting research extending in innumerable directions. Dr C. C. Adams, now of Syracuse University, New York, who has written a most useful work, “the outgrowth of the effort as it has developed in the study and teaching of animal ecology,” in which is listed most of the literature applicable to the science, says (p. 10): “The associational is the phase of animal activity which may be considered as the form of animal behaviour which has developed into the human social relations,” and concludes that, because of the social character of human society, those interested in matters pertaining to the welfare of mankind, such as the sociologist, the physician, the sanitarian, and the agriculturist, will ultimately participate in a keener appreciation of the associational aspect.

For over thirty years problems of stelar structure in the Ferns have claimed the attention of anatomists. By common consent protostely has been recognised as a primitive state. It is seen in all phyla of primitive vascular plants, except the semi-aquatic Equisetales, it figures universally in the juvenile plants of the Filicales, and is maintained in the adult stems of a number of their primitive genera.

But as to the origin of pith, inner phloëm, and inner endodermis, and the steps by which during descent the primitive protostely has in many instances been replaced in the adult by other more complex stelar states, there is no general agreement. On the one hand, the pith, inner phloëm, and inner endodermis have been regarded as purely intrastelar tissues directly referable in origin both in individual plants and descent to the procambial mass of the growing point of the stem.

Isle of Wight Bee Disease has been known in this country certainly since 1904, when it was first recognised in the island from which it derives its popular name. According to Imms it was probably present in Derbyshire in 1902, and was also known in Cornwall and other districts in 1904. Prior to these dates periodic losses of bees of a serious character are on record, dating as far back as the middle of the eighteenth century. Bullamore and Malden (1912) have summarised fully these outbreaks in historical series in their report in Journal of Board of Agriculture, Supplement 8, xix. From a study of the records which they have brought together and from personal inquiries which we have made at various bee-keepers of wide experience, it would appear that none of these earlier outbreaks attained the general distribution throughout the country which we know in Isle of Wight Disease at the present date, nor did any of them remain established over such an extensive period of years as that which has continued without interruption from 1902 until the present time.

A number of rare genera of Ferns of somewhat uncertain affinity had recently come to my hands. As they had by previous writers been referred in some degree to a common relationship it seemed well to embody them together in one memoir. As the work proceeded thejustification of this became more apparent, and towards the end of the work the conclusion seemed clear that the suggested affinities were real though not very close.

Some months ago it was suggested that I should publish my thesis in its unfinished state. I refrained from doing so at that time, as I was unwilling to allow my work to appear until it was ready for publication. When it became apparent that the war. might continue indefinitely. I decided to publish the thesis in such a form as the exigencies of the case would allow.

Considerable interest attaches to the unravelling of the complete life-history of the Psilotaceæ, since they are apparently the nearest living representatives of the Sphenophyllales.

The recent description of the gametophyte of Tmesipteris by Prof. Lawson, whose figures 1 had the privilege of seeing before they went to press, and the discovery of the gametophyte of Psilotum, which is the subject of the present paper, form a first contribution to the solution of this problem. It is of some interest to note that there remains now no Pteridophyte the gametophyte of which has not been described.

In the early part of this research I was fortunate in finding a locality near at hand in which Psilotum flourished, and therefore I had at my disposal abundance of spores and later numerous prothalli.

That the stelar problem considered in this paper may be more clearly visualised, it will be well to divest of purely theoretical considerations the facts of stelar structure already known for Platyzoma, and to summarise such structural features as bear on the subject in hand.

In the first account of Platyzoma given by Robert Brown in 1810 (l), the habit of the stem and heterophyllic leaves, and the general form and position of the sporangia, were alone described. But in 1832 (2) a rough analysis of the structure of the stem was added, and the tubular nature of its stele was recognised. No material contribution to the knowledge of the stelar structure was made until 1893 (3), when Dr Poirault described the histology of the stele as shown by a small fragment of stem. In this material there was a sclerotic pith completely surrounded by an endodermis, outside which lay a zone of parenchyma surrounded by a broad ring of parenchymatous xylem. At the periphery of the xylem there was a narrow zone of phloëm surrounded by a large-celled pericycle and an outer endodermis. Neither leaf-gaps nor perforations were found in the stele, and accordingly the complete isolation of the pith from the cortex was recognised.

Since the preliminary announcement of the discovery of the prothalli of Tmesipteris and Psilotum communicated to the Royal Society of Edinburgh in June 1916, a considerable amount of additional material has been found, and it seems therefore desirable to place on record a more detailed account of these interesting structures. The preliminary description, as published, was based upon but a few specimens, and these were not sufficient to reveal all of the vegetative and reproductive features, nor enough to justify any broad general conclusions as to the phylogenetic position of the Psilotaceæ. The discoyery, however, has filled in an important and interesting gap in our knowledge; for the Psilotaceæ are the very last of the known Pteridophytes to surrender their gametophytes to the light of science.

Several attempts have already been made to interpret the well-established results of biometry in accordance with the Mendelian scheme of inheritance. It is here attempted to ascertain the biometrical properties of a population of a more general type than has hitherto been examined, inheritance in which follows this scheme. It is hoped that in this way it will be possible to make a more exact analysis of the causes of human variability. The great body of available statistics show us that the deviations of a human measurement from its mean follow very closely the Normal Law of Errors, and, therefore, that the variability may be uniformly measured by the standard deviation corresponding to the square root of the mean square error. When there are two independent causes of variability capable of producing in an otherwise uniform population distributions with standard deviations σ1 and σ2, it is found that the distribution, when both causes act together, has a standard deviation . It is therefore desirable in analysing the causes of variability to deal with the square of the standard deviation as the measure of variability. We shall term this quantity the Variance of the normal population to which it refers, and we may now ascribe to the constituent causes fractions or percentages of the total variance which they together produce. It is desirable on the one hand that the elementary ideas at the basis of the calculus of correlations should be clearly understood, and easily expressed in ordinary language, and on the other that loose phrases about the “percentage of causation,” which obscure the essential distinction between the individual and the population, should be carefully avoided.

Isle of Wight disease is, as we have seen, primarily a disease of the respiratory system, in which the organism remains localised throughout the entire course of the attack.

The effects are, however, far-reaching, and are registered in the disordered functioning of several organs, and in visible pathological changes in some of them.

The parasitic invasion has two aspects.

We have, in the first place, to consider the active injury wrought upon the host by a parasite developing and living at the expense of its body fluids. With this aspect of the question may be coupled the possibility of a definite toxic action on the part of the parasite.

In the second place, we have to consider the passive rôle of the mites in hindering or inhibiting the normal functions of the infected organs.

Before proceeding to consider the various pathological conditions, a few words on the distribution of the parasite within the host is called for.

The intrinsic symbol of an amphicheiral knot is based on the idea of the sequence of the crossings; it replaces each letter of the alphabetical symbol by a number equal to one-half of the number of crossings intervening before the next occurrence of that letter as the knot is traversed in a definite direction. Hence it is seen that two knots, which have the same intrinsic symbol, are identical. Since the same number of pairs of crossings must elapse before the next occurrence of corresponding crossings of two identical knots when the knots are traversed in a given direction, it is seen that the converse is true also. It may be necessary to consider the complementary intrinsic symbol in order to detect identical knots.

As the King Penguin chick grows, the down tassels forming the prepennæ increase in length until they measure from 50 to 75 mm. (2 to 3 inches) over the greater part of the body. Some of the barbs of the juvenile down carry for some time natal down barbs on their tips, and the inner ends of all the barbs forming the tassels are eventually found to be continuous with barbs of either the main shaft or the aftershaft of the developing true feathers. How long the down coat is worn by any given King Penguin is not definitely known—it is said that King Penguins may not moult the prepennæ until they are nearly a year old; neither is it known at what time of the year the majority of the King Penguins living under natural conditions in South Georgia shed their prepennæ, or how long the moulting process usually lasts.

The prostates or spermiducal glands form a prominent feature in the anatomy of the large family of the Megascolecidæ. Occurring in the neighbourhood of the termination of the sperm-ducts, they assume one of two forms, the tubular or the lobular. In the first, the gland typically takes the form of a bent, undulating, or coiled tube, cylindrical, with a single central lumen; in the second, it consists of a loosely or tightly packed aggregate of lobules, each with its ductule. The prostatic duct is in the first case a continuation of the glandular tube; in the second, the duct is formed by the union of the ductules; in both cases it is as a rule firm and muscular.

The following experiments and observations have been undertaken with a view to discovering the means by which Tarsonemus is transmitted from one bee to another. It is obvious that a stage of the parasite exists outside the bee, and that there are also several possibilities (which may occur). One is the passage from bee to bee within the hive either directly or through the medium of frames or combs. Another, also within the hive, where the mites may in wandering upon the frames enter the cells and invade the body of the developing larvæ or pupæ, and in this way be present in the bee when it hatches. A third possibility is that whereby foraging infected bees may leave the mite upon flowers, vegetation generally, drinking grounds, or other situations, to be picked up later by other bees chancing to visit these. Crawling or dead bees may in a similar manner prove to be a source of infection through the contamination of the ground about the hive or of the actual hive itself.