Material of a very small and distinctive species of Isoetes was sent by Miss Alison Baird in 1934 to Professor J. Walton, who kindly handed it over to me for examination. This species, hitherto undescribed, is here named Isoetes australis. The material, which consisted of plants of all ages from two-leaved sporelings up to adult plants, had been collected in 1930 from rock pools in granite outcrops at Bruce Rock, 150 miles inland from Perth, Western Australia.

The following description is mainly based on Miss Baird's material, but I later received air-dried plants of the same species which had been grown by Professor T. G. B. Osborn in the Laboratory at Sydney. These plants had originally been collected by E. T. Bailey from the Bruce Rock locality in 1934. They proved to be viable and commenced growth within a few days when placed in water, and I was able to keep one of them alive for a period of two years, though only in a depauperate condition. Professor Osborn also sent me herbarium specimens, collected in the same locality by Bailey, and some of these plants, which had been completely dry for six months or longer, proved viable, though I was unable to grow them on for more than a few months.

The Race A/Race B hybrid females of D. pseudo-obscura have a high percentage of fertility, comparable with that of females of pure race. The number and viability of their offspring, however, are largely affected by the genetic constitution of the hybrid female as well as by that of the male to which she is mated in the backcross. Hence the performance of any given hybrid is determined in the first instance by the actual strains of the pure races which are used in making the P1 racial cross. Generally speaking the results are of the same order whenever the same strains are used. The progenies of hybrid females of different genetic constitution may differ in three main aspects: (1) The total number of offspring may be comparable with that usually obtained in a pure race cross; it may be reduced to any extent; in certain matings it is consistently at zero. (2) The sex ratio may be completely normal or male-deficient or female-deficient in any degree; completely uni-sexual progenies are sometimes obtained. (The above observations are mainly in agreement with reports of earlier writers; cf. Lancefield, 1929, Dobzhansky, 1936, Mampell, 1941, Sturtevant, 1937.) (3) “Viability characters,” i.e. those affecting general vigour and physical normality, may be of a high or a low grade; some progenies are comparable in this respect with the pure race, the only exception being that they show a much greater range of variation in body-size of both sexes, and in the testis size of males, abnormalities which are common to all back-cross progenies whatever the genetic constitution of the mother or father. Some progenies show in addition deformities of a peculiar type usually affecting the abdomen and occasionally the legs and wings.

In two earlier publications the author has suggested a theory of genetically determined asymmetries. Inherited asymmetry may be of two types. Many characters are unilateral (e.g. the aortic arch or the tricuspid valve of the human heart) or in some other way placed asymmetrically (e.g. the differentiation of organs along the cephalad-caudad axis of the body). The orientation of such gross asymmetries is in general irreversible. The author has pointed out that the study of uniovular twins which exhibit mirror-image similarities draws attention to a smaller class of reversible asymmetries. While an asymmetrical disposition of such a character is transmitted, its orientation is not fixed in the process of transmission. Thus a character may show itself on the left side in one generation or in one individual of a litter, and on the right side in another generation or in a litter mate. The extreme types of variation between which many transitional forms may be found are:

(a) From left to right, or vice versa.

(b) From caudad to cephalad extremity, or vice versa.

(c) From dorsal to ventral surface, or vice versa.

According to Ellerman (1941), the seventy-odd forms of palæarctic rodents that go under the name of “True Hamsters” (family Murinæ, subfamily Cricetinæ) fall into four genera with a total of 18 species: Cricetulus (11), Phodopus (3), Cricetus (1), and Mesocricetus (3), the last two genera being unified by some authors. So far only one species of this important group has been investigated from the point of view of chromosome properties: the Golden Hamster, Cricetus (Mesocricetus) auratus Waterhouse.

Electroencephalography has added another important means of investigation of cerebral activity and functioning to the many others previously at our disposal. In applying it, as with the other investigative methods, it is important that we should have clearly in mind exactly what facts it is able to demonstrate and what interpretations we are justified in making of the observed facts. This process of interpretation is difficult partly because it is a two-stage one; the electrical potentials observed are those on the surface of the scalp and these must first be referred back to potential sources (i.e. electrical charges) in the brain itself. These latter must then be interpreted in terms of activities of nerve cells and nerve fibres. The first of these two stages belongs entirely to the sphere of mathematical physics, and the present paper is an attempt to present a working hypothesis which not only suggests a solution of this stage of the problem, but suggests a probable solution of the second stage. The second stage properly belongs to the sphere of physiology, but progress here is rendered difficult by lack of decisive knowledge as to the nature of the elementary unit of central nervous activity.

In common with other neoplasms, the Rous No. 1 tumour often shows small areas or even single cells that appear dead and disintegrating or moribund. These probably result from the interaction of such factors as inadequate vascularization, pressure, and the formation of non-viable cells as a result of abnormal mitosis. As death of the cell does not necessarily result in destruction of the tumour virus, the virus of such cells is presumably released into the host's tissues. There is some difference of opinion as to the part that this virus plays in extending the growth of the tumour by infecting neighbouring cells and by producing metastases (review in Foulds, 1934), but it is generally agreed that the virus is present in most tissues of an animal bearing a filterable tumour (Bürger, 1914; Fujinami and Suzue, 1925; Fränkel, 1927; Costa, 1932; Mellanby, 1935, 1936, 1937, 1938 a, 1938 b) without, however, producing any tumours. The reason for this absence of carcinogenic action on the part of the disseminated virus has remained obscure. It was also noted that recurring Rous tumours are always found at the sites inoculated with tumour material, and never result from disseminated virus (Carr, 1942). Mellanby (1938 b) noted that the amount at first increased and later decreased with time, no active virus being found forty or more days after the initiation of tumour growth in the host. A similar decrease in the amount of extractable virus in tumours has been described (Carr, 1943) and shown to be due to antibodies in the tissue fluid inactivating the virus as it is extracted from the tumour cells. This raised the possibility that virus was similarly present in the normal tissues of hosts bearing lasting tumours, though not demonstrable for the same reason. The present investigation was undertaken to see if this was the case, and to discover the reason for the absence of neoplastic action of such virus.

The frequent reports of 20 per cent, or more losses due to neoplastic diseases in poultry flocks indicate that this is one of the greatest troubles of the industry. Though certain of the avian tumours have been favourite subjects for experimental cancer research, little attention has been directed to the problem of the ætiology and control of avian cancer itself. Consequently, despite the urgency of the problem, there is little information available which can be used as a basis for prescribing any preventive measures. It is not even known whether the majority of the spontaneous tumours are induced by a virus. Not many attempts have been made to transplant and study these tumours, considering the wealth of material available; and only a small proportion of the attempts have succeeded. Though most of these successfully transplanted sarcomas were found to be associated with a causative virus, it is impossible to state whether this is the usual condition of spontaneous tumours, or whether the few successful transplants were aberrant forms whose associated virus altered the growth characteristics and thus enabled a successful transplant to be made more easily.

According to Grollman (1936), there is no evidence for an intimate relation between the gonads and the adrenal proper, i.e. the cortex apart from the “fœtal zone” (Grollman, 1942). Recent papers, however (Bourne and Zuckerman, 1940 a, 1940 b; Schilling and Laqueur, 1941; Selye and Albert, 1942; Selye, Rowley, and Hall, 1943; Sarason, 1943, and others), confirm the opposite view (Kolmer, 1912; Korenchevsky, Dennison, and Simpson, 1935). The results, especially those concerning the action of gonadal substances on the adrenal cortex, vary as between different authors and according to the species of experimental animal used. Grollman (1936), for example, states that the cortex is not influenced by œstrogen. Allen and Bern (1942), however, and Golla and Reiss (1942) report a change in the cortex associated with an increase of adrenal weight. The former authors found an increase in lipoid-containing vacuoles in guinea-pigs treated with stilbœstrol; the latter, on the other hand, observed a lipoid decrease in rats treated with œstrone. Comparison of these results with others which they obtained with hypophysectomized rats even led Golla and Reiss to postulate the existence of two corticotrophic principles in the hypophysis: one controlling the distribution of lipoid in the cortex and the other the adrenal weight.

The Bunsen-Roscoe law states that the effect of radiation is always the same regardless of the variation in the intensity or in the time of radiation as long as the product of the two is kept constant. This law holds true for many ordinary physico-chemical reactions over a wide range of intensities. The present investigation was undertaken to test the validity of the Bunsen-Roscoe law by studying the frequency of (1) sex-linked lethal mutations and (2) translocations in Drosophila melanogaster at much lower intensities of radiation than those previously tried.

It was in 1878 that Ehrlich, with the aid of his triacid stain, described in terms of granulation of the cytoplasm six types of leucocytes. This marked the first real advance in our knowledge of the blood corpuscles. Present-day classification of cells in the blood-forming tissues gives six main groups with about thirty named types of cells. These fine subdivisions appear to represent different stages in different lines of development from one original type, chiefly by change in the shape of the resting nucleus. Divergence in opinion arises as to whether all these types of cell develop in the red bone marrow, or whether some arise elsewhere in the body.

Some years ago the British Association for the Advancement of Science standardised the methods for the determination of the measurements of length, breadth, and height of the living head or dead skull, but said nothing about the brain. But to-day we know that these same methods can also be used for the measurement of the post-mortem brain. The advantages of having one common series of measurements for the living head, dried skull, and post-mortem brain, and one standard mode of comparing the results are so obvious as to need no further justification.

The classical view that, of the two known types of nucleic acid, desoxyribonucleic acid (thymonucleic acid) is characteristic of animal tissues and ribonucleic acid (pentose nucleic acid) of plant tissues, was established by the work of Kossel and others and upheld as a fundamental generalisation by Jones (1920). This view, which was current for over thirty years, has had to be abandoned in the light of more recent evidence. Not only has desoxyribonucleic acid been found in plant tissues, but ribonucleic acid has been isolated from the pancreas (Jorpes, 1928, 1934) and has been shown to be widespread in animal tissues (Davidson and Waymouth, 1943, 1944 a, b). Ribonucleic acid has been isolated, also, from liver tissue, in which it is present in much larger amounts than is desoxyribonucleic acid (Davidson and Waymouth, 1944 c).

Examination of mammalian pelts reveals the presence of two types of hair—long, glossy fibres known as “guard”- or “top-hair,” and shorter, softer, more curly fibres termed ”ground”- or “under-wool.” Guard-hairs are of two kinds: primary fibres classified by Toldt (1910) as “Leithaare,” and shorter, less robust secondary fibres which Toldt described as “Grannenhaare.” The under-wool is analogous to Toldt's “Wohlhaare.” More recently Toldt (1935) has described the appearance of the various fibre types occurring in hair from a wide range of mammals, and gives an extensive bibliography on hair from many orders of mammalia, including the two at present under consideration. Glaister (1931) made a photomicrographic survey of whole mounts and transverse sections of fibres from a large number of mammals. This work, however, suffers from the disadvantage that the photomicrographs were taken at low magnifications. When photographed at magnifications of the order × 500, transverse sections of fibres readily demonstrate the distribution and structure of cuticle, cortex and medulla. Such information is valuable as a means of studying structural variations in hair from different types of mammals, and often possesses considerable taxonomic significance and practical value—Dearborn (1939) reports the use of cross-sections of mammalian guard-hairs as a help to identifying small hairs found in the stomachs and excreta of predators, while the importance of fibre histology in forensic science has been reviewed by Smith and Glaister (1939). Furthermore, microchemical tests carried out on wool fibres (Bekker and King, 1931) and on transverse sections of kolinsky and hare fibres (Stoves, 1943 a) have shown that cuticle, cortex, and medulla exhibit different chemical properties, so that morphological differentiation is accompanied by variation in chemical reactivity.