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 present paper is the third of a series of studies on the coccidia of Indian birds, and contains the description of six new species of these parasites, four of which belong to the genus Isospora, and one each to the genera Dorisiella and Eimeria, All the parasites described here belong to the Order Coccidiida, Family Eimeriidae. New avian hosts for some already known species are recorded here. The life-history of Eimeria barbeta Kar (1944) is described in detail. We also add here an amended description of Isospora ginginiana Chakravarty and Kar (1944 b), and a new variety of the latter.

The majority of the birds were purchased from local dealers, while some were collected from Gaya, Bihar. Of twenty-eight different species of birds examined, eighteen were parasitized. The table at the end of this paper will indicate the number of birds parasitized (21) out of the total number examined (48), together with the locality of the hosts. Some of the birds were also infected with other protozoan parasites (haemosporidians and flagellates), descriptions of which are being published elsewhere.

The methods adopted here are the same as previously employed by the authors (Chakravarty and Kar, 1944 a and b).

Two species of birds, viz. the large Indian paroquet Psittacula eupatria nipalensis (Hodgs.) and the red-whiskered or Chinese bulbul Elathea jocosa emeria (Linn.), harboured a new Isospora, which does not resemble any known species of this genus. It is therefore proposed to call it Isospora psittaculae n. sp. after one of its hosts.

Taking the mammalia as a whole, there are two principal forms of digestion; the first is by means of the juices which the wall of the gut secretes, and which reduce the food to a form absorbable by the wall of the alimentary canal; the second is by means of organisms contained in the alimentary canal, which not only can perform a similar function, but which, by multiplying in the gut at the expense of the foodstuffs, can themselves form diet more nutritive than that in which they grow. In one way or another the organisms can convert materials in their food, which otherwise would be wasted, into articles of diet important to the animal in whose gut these lowly creatures thrive.

The present paper forms a continuation of studies of recessive sex-linked lethals in Drosophila melanogaster published previously (1938, 1941). In these, lethals occurring spontaneously, induced by X-ray treatment and by ultra-violet light were examined cytologically in the salivary gland chromosomes.

The genetic factors which stop or change the development of an individual in such a way that its death ensues under normal conditions are termed lethals. A lethal effect may be connected with a mutation of a gene or with its absence from the chromosome: those which cannot be proved to be associated with the absence of a cytologically detectable part of the chromosome are considered as due to “point” mutations.

The absence of a microscopically identifiable section of a chromosome with all its genetical and structural elements is called a deficiency. With few exceptions (Muller, 1935; Demerec and Hoover, 1936) the deficiencies in the X-chromosome, whatever their size and whatever loci they involve, are lethal for males. In females heterozygous for them deficiencies of small or even moderate size usually do not produce any visible phenotypical effect, although some cases are known (Mohr, 1923; Slizynska, 1938) in which a heterozygous deficiency for a particular band is always associated with a definite phenotype. Thus a lethal effect may or may not be the result of a deficiency, while a deficiency in the X-chromosome almost always has a lethal effect in the males.

In 1941 Auerbach (1943, 1946 in press) succeeded in producing “visible” and lethal mutations and chromosomal rearrangements by chemical treatment in which adult males were exposed to vapours of (C1CH2CH2)2S in a specially designed apparatus. The object of this paper is to show what proportion of sex-linked recessive lethals produced in Drosophila melanogaster by these new agents is connected with detectable deficiencies. Besides finding out whether chemically produced lethals are associated with detectable deficiencies, the problem of the relation between lethals and “visible” mutations is discussed on the basis of their respective distributions along the chromosome. It should be stated that the lethals connected with gross structural changes represent probably only a small fraction of such lethals actually produced since many of them were eliminated by zygotic lethality.

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.

The problem to be presented here emerges from the following groups of facts and more or less generally accepted opinions.

As heterochromatin we may define those parts of chromosomes which reach maximum nucleic acid charge in mitosis or meiosis in times other than metaphase. In salivary gland chromosomes (which are more conveniently called polytene chromosomes) of Drosophila melanogaster the proximal heterochromatic parts of all chromosomes come together and form a central undifferentiated mass, the chromocentre. Genetically heterochromatin forms the so-called inert regions of the chromosomes.

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.

The mechanism by which irradiation produces gross re-arrangements of chromosomes (inversions, translocations, deletions) is now generally believed to occur in two steps: (a) breakage of one or more chromosomes, yielding two or more points of breakage; and (b) reunion of broken ends in a novel combination. Thus the frequency with which a given treatment produces re-arrangements depends not only on the number of breaks produced, but on the circumstances under which reunion takes place. In Drosophila the fertilized ovum seems to offer particularly favourable conditions for breaks produced in the mature spermatozoon to join up into new combinations. In immature germ-cells, on the other hand, re-arrangements are much less readily produced by irradiation (Muller, 1930; Shapiro and Neuhaus, 1933; Shapiro, 1937; Glass, 1939). Evidence for the occurrence of spontaneous or induced re-arrangements in somatic cells of Drosophila is very scanty.

For many years now the filterable viruses have been considered as a possible cause of cancer, though such a theory has never found favour with the majority of pathologists. Definite proof of a causative virus has in turn been found for many avian tumours (review in Foulds, 1934), rabbit fibromas (Shope, 1932), rabbit papillomas (Shope, 1933), frog kidney tumours (Lucké, 1938), and the mammary tumours of mice (Bittner, 1937), and there is some evidence that certain other mouse tumours may depend on the presence of a milk-transmitted factor similar to that responsible for the mammary carcinomas first investigated. Many experiments have been carried out by numerous workers to demonstrate a causative virus in other types of neoplasms, but usually with negative results, and the successes sometimes claimed have not been confirmed by other workers. Negative results such as this are always unsatisfactory when, as in these cases, the true ætiology is unknown, and arguments for and against a virus-like entity as a cause of cancer continue to be urged by both sides. Two excellent modern statements of the case for a virus ætiology of neoplasms are given by Rous (1943) and Oberling (1942). An essential point in this argument is to offer reasons why the virus may be difficult or impossible to demonstrate in spontaneous neoplasms. Among these may be mentioned Andrewes' (1939) conception of a non-infective “toothless” virus; another is the well-known fact that even the classical virus-induced tumour, the Rous No. 1 sarcoma, often produces tumours in which it is impossible to demonstrate the presence of the virus (e.g. Gye and Andrewes, 1926; Carr, 1942, 1944).

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.

In studying the literature relating to that little-known prosimian, the Angwántibo—with a view to incorporating the main facts known about it in a comprehensive work on primate anatomy at present in preparation—I had occasion to consult the original description of the species by J. A. Smith (1860). I there discovered that the type was a spirit specimen (an “adult” male) which was received in Edinburgh, along with a second male, from Old Calabar. There is some confusion in the literature as to the fate of these specimens and this should, I think, be cleared up. Both specimens were procured in 1859 by Rev. A. Robb, one being sent, indirectly, to Smith and the other to Andrew Murray. Smith recognized in his specimen something new and accordingly described it as a new species of Potto, placing it in Bennett's genus Perodicticus as P. calabarensis. He gave an assurance of his intention of depositing the type in the Natural History Museum of the University of Edinburgh, but later sent it to his friend Carruthers at the British Museum for comparison with Bennett's type of Perodicticus potto. Some useful observations were made upon it by Carruthers and incorporated as an addendum to Smith's paper. The specimen was evidently returned to Edinburgh and found its way to the University, but in 1860 it was transferred, with other material, to the Edinburgh Industrial Museum (since 1904 the Royal Scottish Museum).

With the kind assistance of Professor J. Ritchie I have succeeded in tracing it, and with the permission of Dr D. A. Allan, Director of the Museum, and the helpful co-operation of Dr A. C. Stephen, Keeper of Natural History, I have had the privilege of studying it.

A Summary of the facts with numerical details omitted can be given as follows. In the diatoms—

1. Species-lifetimes have been alternatively short or long.

2. The main ratios of shorts to longs, or evanescents to permanents, e/p, are 3:1 for Centrales, 10:6 for Fragilariaceæ, 7:9 for allogamous Pennales. These ratios or nearest approaches to these ratios occur in the above three groups, (a) in each group as a whole; (b) in species-arising in each group per geological subperiod; and (c) in heterogeneous genera in each genus as a whole and in each genus per subperiod. A derivative 1:3 ratio also occurs in some pennate genera. There are some significant and understandable exceptions.

In 1859 Andrew Murray, an Edinburgh naturalist, described, under the name of Galago murinus, what he believed to be a new species. His account was based upon material from Old Calabar sent to him by a missionary, Rev. W. C. Thomson, who had kept the animal some time in captivity. Murray was, at first, undecided whether to allocate his specimen to one or other of the two previously known smaller Galagidæ, namely G. senegalensis or G. demidovii, and sought the advice of Gray, who thought it probably a juvenile Senegal Galago. (The more usual rendering demidoffi was shown by Schwarz (1931) to be incorrect, the first usage as a Latin name being demidovii (G. Fischer, 1808).) Murray did not accept this opinion, for he considered his specimen an adult, though not old, because its fontanelles were closed. He specified the distinctions from senegalensis as follows:—

(a) Small size, it being only half the size of the larger species, declared by the missionaries (Thomson and Robb) to inhabit the same locality.

(b) Difference in colour—mouse-coloured instead of the “orange-tawny-yellow” of senegalensis.

(c) The nakedness of the ears.

(d) The long fourth digit of the hand (according to Audebert's (1801) figure of senegalensis, the third was supposed to be longest in that species).

(e) The slenderer, less bushy tail.

All the above are perfectly good reasons for separating murinus from senegalensis and its allies, but, unfortunately, Murray gave no reasons against its being identified as demidovii, previously known from Senegal, but erroneously believed by Murray to come from Madagascar and hence, probably, regarded as a justification for distinguishing it from murinus.

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.

During a study of the micro-structure of keratin fibres (Stoves, 1944) it was found that certain members of the Mustelidæ, e.g. kolinsky (M. Sibirica), ermine (M. erminœ), and Jap mink (M. itatsi), possess primary hairs with well-developed cuticle, cortex, and medulla. In the case of rabbits and hares (Leporidæ), however, the corresponding fibres are composed almost entirely of medulla cells. The two types of fibres, therefore, provide suitable material for studying the chemical reactivity of the keratin constituting cuticle, cortex, and medulla of animal hair. Accordingly, the effect of various reagents upon transverse sections of fibres from the above-mentioned animals was examined, and a preliminary report of the results has already been made (Stoves, 1943 a). A more detailed account of the work now appears.

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 production of mutations by the action of chemical substances on germ cells has often been reported. However, the variability of the spontaneous mutation rate and its dependence not only on environmental conditions and physiological factors, but also on the genotype, make it extremely difficult to assess the value of tests in which only small increases over the spontaneous mutation rate have been found. For this reason, Muller was still able to conclude in 1941 that there was no definite proof that chemical substances could exert an effect on the mutation rate. Since then, Thomas and Chevais (1943) have reported results with sulphonamides which, if they can be confirmed, would indicate a real, though slight, action of these substances on the chromosomes, at least as far as gene mutations are concerned. Stubbe (1940), working on plant material, observed a significant increase in mutation rate with phenol and potassium thiocyanate. It is of interest that Auerbach and Robson (1943) independently observed a similar effect with allyl isothiocyanate in experiments on Drosophila. Even these definite effects are, however, very slight.

During the last four years we have been testing a number of chemical substances. Among these a certain group has been found which increases the rate of occurrence of mutations and chromosome rearrangements to a similar extent as that brought about by X-rays and similar physical agencies. The best known representative of this group is mustard gas, and the present report deals only with the effects produced by this substance. Results obtained with other effective substances will be published later.

The work recorded in this paper was undertaken in order to obtain further knowledge regarding the behaviour of the cytoplasmic components of the male germ-cells of mammals and the contribution made by these bodies to the structure of the ripe sperm. Consequently, mammals from different groups were examined.

Investigations were carried out independently by Zlotnik on the male germ-cells of the dog, the cat, and the rabbit, by Gresson on the boar and the ram, and jointly by Gresson and Zlotnik on the white rat and the golden hamster. Zlotnik (1943) originally identified and described the nuclear-ring of the spermatid and sperm of the dog. The accessory body was recognised simultaneously by him and by Gresson, but Zlotnik was the first to observe an accessory body within the localised Golgi material of the spermatocyte and to follow its extrusion to the cytoplasm, and, later, Gresson identified an accessory body within the Golgi material of the spermatid of the boar. In general the conclusions of the two authors are closely similar, such differences of detail or of interpretation as exist are discussed in this paper.

The discovery in 1941 (Auerbach and Robson, first published in 1946) that mustard gas (β-β′-dichloro-diethyl-sulphide), (ClCH2.CH2)2S, is comparable to X-rays in its capacity to produce mutations and chromosome rearrangements naturally raised the question as to what special properties of mustard gas enable it to act in this manner. There are indications (Auerbach and Robson, 1947) that the mutagenic effects of mustard gas are due to a direct action on the chromosomes, and not to an indirect one via the cytoplasm. This suggests that a selective and specific chemical reaction occurs between mustard gas and the genie material. It appeared possible that a systematic survey of substances chemically related to mustard gas might reveal a chemical group or structural arrangement responsible for the mutagenic action. This in its turn might also throw some light on the other component of the reaction, the gene or chromosome, and on the process of mutation itself.

The substances, to be tested were, with one exception, chosen on account of their chemical and pharmacological similarity to mustard gas. They were:

(1) N-methyl di-(2-chloroethyl) amine, CH3.N(CH2.CH2Cl)2, one of the so-called nitrogen mustards. This is a liquid with strong vesicant action. It decomposes fairly rapidly in water. Its hydrochloride is a solid, soluble in water and forming a stable solution. This solution proved useful in certain tests in which it was convenient to apply a mutagenic substance in aqueous solution.

Studies of the inheritance of resistance to two strains, A and B, of the blight fungus (Phytophthora infestans) in derivatives of the triple hybrid (S. Rybinii x S. demissum) x S. tuberosum and in hybrids descended from S. demissum x S. tuberosum led to the conclusion that resistance was controlled by two genes, designated Ra and Rb, of different phylogenetic origin, the former conferring resistance against strain A and the latter against both strain A and strain B (Black, 1943).