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.

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.

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).

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.

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.

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 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.

The Acrididæ are characterised by a very uniform karyotype. With a few exceptions, the species so far studied contain 23 chromosomes in the male, which are very similar in size and structure. Attempts to deduce the probable mechanism of speciation within the Acrididæ were restricted only to metrical studies of chromosomes. Recently, however, Coleman (1943) has established in two species the subterminal position of the primary constriction or centromere and the variation in the length of the two arms in different chromosomes of the same karyotype. In the present paper additional evidence is presented which shows a linear differentiation of some chromosomes of the Acrididæ. Furthermore, in view of the fact that chromosome behaviour during meiosis is a more reliable criterion of ascertaining linear differentiation, the meiosis was studied in three genera.

Three species belonging to three different genera were studied. They are Spathosternum prasiniferum Walker, Oxya sp. and Phlœoba sp. The former two belong to the sub-family Catantopinæ and the latter one to Acrididæ. Adult male specimens have been captured from the field adjoining the Biological Departments, Calcutta University, mostly in the months of August and September 1943–44. The testes were dissected out in Ringer's solution (cold-blooded formula) and fixed in Medium Flemming, Belling's, and Kahle's fixatives. The two latter were very suitable for smear preparations. Sections were cut at 25 to 30 micra in thickness and stained in iodine-crystal violet and in Heidenhain's hæmatoxylin. A 2 per cent, solution of safranin also gave good results. Squash preparations were stained by Feulgen's method. Diplotene stages in Phlœoba were studied from temporary aceto-carmine preparations.

Heterokaryosis is the condition in which one cell of a mycelium contains two or more genetically different nuclei. Hansen and Smith (1932), working with Botrytis cinerea, which has multi-nucleate spores, showed that single-spore cultures of this fungus sometimes contained two types of nuclei and that such heterokaryotic types could readily be induced by hyphal fusion between different homokaryotic types. These authors analysed individuals from thirty genera of imperfect fungi and found more than half of them to be heterokaryotic. It seems, therefore, that heterokaryosis is a widespread phenomenon among such fungi.

N. crassa is a heterothallic fungus with an eight-spored ascus and a pair of well-defined mating-type factors which have been very generally called sex factors. Perithecia are formed only when cultures of the opposite mating types are brought into contact. Both mating types can produce ascogonia, generally conceived to be female organs, and microconidia, sometimes called spermatia (Dodge, 1935), which may correspond to male gametes. Therefore it is doubtful whether the mating-type factors are true sex factors.

A non-committal term such as “mating type” or “incompatibility factor” is preferable. However, because of the convenience of the terms associated with sex, such as “unisexual” and “bisexual”, I shall follow previous authors (Dodge, Lindegren, Beadle) in using these terms with reference to the mating-type factors, at the same time emphasising that these factors may not be sex factors in the generally accepted sense of the term.

An account was previously given of the discovery of two cases of placental fusion in mice, and it was suggested that this condition might occur fairly frequently. This has been amply borne out by subsequent experience, as fourteen other examples have been found while working with mice, and in addition it has once been found in the rat. From this additional material further information about the types of developmental abnormalities that may result from this condition has been gathered. Since the last paper, Owen (1945) has found that commingling of the fœtal circulations in cattle twins can result in the transfer of erythrocyte precursors between partners, resulting in animals exhibiting blood-groups bearing no relation to their genotype. Similar transfers in mice would lead to confusion in many genetic experiments, especially in transplantation experiments with tumours.

No genetical basis for the condition is apparent from the data available. It has been, noted in three matings of CBA mice, two of C3H mice, eight C3♂ × CBA♀, and three stock mice, the proportions being roughly related to the relative numbers of each type examined at the time of littering. The frequency is rather less than 1 per cent, of all placentas seen. The only common feature, to which attention was also drawn in the previous paper, has been that the fusion occurred always in conditions of uterine crowding due to large litter size. The smallest litter size in which this fusion was found was five, but in this case five placentas were present in one horn. Whenever labour was observed, it appeared to be difficult and prolonged. Once, by good fortune, delivery was timed approximately. A CBA mouse was found to have delivered two young, and two more were born within the next ten minutes. Nothing further appeared for two hours and ten minutes, when a live pair with fused placentas was delivered with some distress. The last two of the litter, making eight in all, were delivered within twenty minutes of the completion of the birth of the fused pair

The discovery (Auerbach, 1943, 1946; Auerbach and Robson, 1946, 1947) that mustard gas is comparable to X-rays and similar physical agencies in its ability to produce mutations and chromosome rearrangements has opened up a new line of approach to the problem of gene mutation. It is to be expected that a comparative study of the mechanism by which chemical substances on the one hand and physical agencies on the other exercise their mutagenic effects, will further our understanding of the process of mutation itself. One of the first questions to be tackled in the early days of radiation genetics was the possibility of a delayed mutagenic action of irradiation (Muller, 1927; Timoféeff-Ressovsky, 1930, 1931; Grüneberg, 1931). The bulk of the evidence (see, however, Bishop, 1942) indicates that X-ray-induced mutations and chromosome breaks arise as an immediate effect of the irradiation, although after treatment of mature spermatozoa new recombinations of broken chromosomes may be delayed until the spermatozoon has entered the egg. Data obtained by Stadler (1939) suggest that after ultra-violet radiation of pollen grains the mutational process often is not completed before the treated chromosome has split into its two daughter chromatids. This results in a high proportion of mosaics. A similarly high proportion of mosaics has been found in the progeny of Drosophila ♂♂ which had been treated with mustard gas (Auerbach, 1946; Auerbach and Robson, 1946). This raises the question of a possible delayed action of the chemical mutagenic treatment.

According to Borst (1913) each individual should be regarded as a specific biochemical system, and within this common background the different organs and tissues work together whilst preserving their own characteristics. On such a foundation, strengthened by the results of his own extensive experiments, Loeb (1930,1945) has built up his conception of the biological basis of individuality. According to his thesis the individuality of a tissue is a summation and integration of qualities in respect of its identity as a particular tissue or organ, in respect of the organism of which it is a part, and in respect of the species and order of this organism. The autograft is attuned to the biochemical system of the organism and is therefore accepted as a transplant, but the host reacts to the homograft (and more so to the heterograft) and makes an effort to destroy it. While the extent of the host reaction depends on many factors—e.g. genetical relationship, age of host and donor, etc.—the ability of different organs and tissues to survive as homografts varies considerably. It is, for example, well known that homografts of cartilage and cornea survive within the host long after homografts of other tissues and organs have been destroyed.

To regard the more prolonged survival of homografts of cartilage and cornea as evidence of low tissue specificity (Loeb, 1930, 1945) still leaves undetermined the real reason why these particular tissues are less readily overwhelmed by those of the host.