Abstract: SERIES of recent papers (DOBZHANSKY 1935; DOBZHANSKY and A TAN 1936; DOBZHANSKY 1937)) has described the unusual and interesting features which characterize the breeding behavior of Drosophila miranda and especially its method of sex determination. These papers have also reported the results of hybridization of miranda with the closely related and better known species, Drosophila pseudoobscura, and have given a detailed description, based on the study of the salivary gland chromosomes of the hybrids, of the similarities and differences in gene arrangement in these two species. In spite of these studies, there remained much that was obscure about the operation of the sex-chromosome mechanism, and particularly about the manner in which such an organization of the sex-determining material could have been derived from the more familiar sort'found in D . pseudoobscura and, indeed, throughout the genus Drosophila. Because of the need for more information on these interesting points, PROF. DOBZHANSKY suggested that I attempt to review and extend his observations. For this, for his kindness in furnishing me with stocks used in the investigation, and for much helpful criticism, I wish to express my gratitude to PROF. DOBZHANSKY. Helpful suggestions for the revision of the manuscript have been kindly given by PROF. F. R. IMMER and PROF. C. R. BURNHAM. To PROF. A. H. STURTEVANT, under whose direction this work was performed, I am deeply indebted for advice and encouragement. The studies here reported have been sufficient to render more understandable the operation of the sex-determining mechanism of Drosophila miranda, and to indicate the manner in which it has been derived from the type present in the common ancestor of pseudoobscura and miranda.

Abstract: HE general problem of chromosomes and speciation has interested T cytologists and geneticists for a long time. The earlier studies on animals dealt with comparisons of the metaphase chromosomes, and evidence for homologies in related species was restricted to a similarity in chromosome number and to the appearance of the individual elements. Following MULLER’S X-ray work and the discovery of numerous chromosome rearrangements, the judging of homologies by comparing metaphase elements appeared hazardous because it became clear that very extensive gene realignments may occur without one’s being able to detect them in the condensed chromosomes. In addition to this, the presence of inert chromatin (MULLER and PAINTER 1932) could make such comparisons very misleading. PAINTER’S discovery and development of the salivary gland method for the study of chromosomes, opened a new era for the cytologist. He pointed out in his first paper (1933) that homologous chromosomes undergo somatic synapsis, and due to this phenomenon it is possible to compare in the most exact way the “active” or euchromatic areas in salivary gland chromosomes. In closely related species which can be hybridized one should be able to detect any chromosome rearrangements which might have occurred since the related forms originated from a common ancestor. The salivary gland chromosome method has been employed thus far in the study of three species crosses. The first of these is the Drosophila melanogaster and D . simulans cross reported by PATAU in 1935. He found that with a few exceptions there is usually close synapsis in hybrids in the euchromatic areas. The distal ends of some of the chromosomes do not conjugate. There are two extra lines in the X chromosome of D . simularts which are not seen in D. melanogaster, and in the right arm of the third chromosome there is a long inversion, reported earlier by STURTEVANT (1929) who based his conclusion on genetic data. PATAU also noted that a part of the non-inverted proximal end of the right arm of the third chromosome failed to synapse and that the fourth chromosomes were entirely different and would not conjugate in hybrids.

Abstract: ARAMECIUM bursaria is one of the most widely distributed of P the species of Paramecium, though it does not as a rule occur in such large numbers in a given region as does sometimes Paramecium caudatum. It occurs commonly amid growing vegetation in the quiet parts of pools, ponds or streams. It does not flourish in regions in which the water is foul or there is much decaying vegetation. ’ The species is commonly at once recognizable by the algal cells which it contains, which give it a green color. The algal cells are usually packed closely, but a t times they are few and scattered or perhaps even nonexistent, so that the animals are nearly white. Such white individuals may readily be produced by allowing the animals to multiply rapidly in a rich culture medium. The ciliates then multiply more rapidly than do the algae, so that the animals are left with almost none of the algal cells. Figures and descriptions of this species in comparison with others are given by WENRICH (I 9 28) , KALMUS (I93 I) , and KAHL (I 93 I). Many diverse biotypes occur, which may differ greatly in form, size and physiological characteristics. The typical form is more flattened, “slipper shaped,” than in Paramecium caudatum or aurelia. The flattened body is slightly curved in a segment of a flat spiral, the broad oral groove extending on one surface from the anterior end to about the middle of the body. The anterior tip projects forward, to the right, and a little downward (toward the oral surface) ; in very pronounced cases this gives almost the appearance of a hook. Typical forms and sizes for certain biotypes are shown in outline in figure 7 on page 225. As there illustrated, the length ranges from about IOO microns (in the clone 1 figure 7, 2) to about 160 microns or a little more, in a clone of the type E from California (figure 7, 12). Paramecium bursaria has been much employed in genetic and physiological investigations. The earlier studies on it are resumed by MAUPAS (1889, pp. 228-238), who himself studied the nuclear processes in conjuga-

Abstract: MONG the widely divergent results obtained from “quantitative A character” crosses one common type is characterized by (a) F1 mean approaching that of the smaller parent strain and (b) positive skewness in the frequency distribution of Fz measurements. Among many examples might be cited crosses involving differences of corolla tube length in tobacco (EAST 1913; SMITH 1937), fruit size in squash (SINNOTT 1937) in peppers (DALE 1929; KAISER 1935) and in tomatoes (MCARTHUR and BUTLER 1938), weight in chickens ( JULL and QUINN 193 I). Results of this kind have long been recognized as incompatible with the early hypothesis that quantitative characters might be determined in general by genes having arithmetic effects without dominance or interaction. This hypothesis had been proposed (EAST 1910) as a reasonably simple scheme which might and did accord with the main features of size segregation in certain crosses. But other crosses, giving the sort of result under discussion here, were shown by EAST (1913) to be better accounted for if the relevant genes were assumed to have a multiplicative, or geometric, action. Many subsequent workers have adopted the same interpretation for comparable cases (DALE, SINNOTT and SMITH, among others). LINDSTROM (1935) has proposed a partial return to the original hypothesis, in dealing with skewed distributions of fruit size in the progeny of hybrids between a small-fruited wild tomato and two large-fruited domesticated varieties, namely: that the factors have arithmetic effects, without interaction, but with partial dominance of the small size genes. In discussing his results LINDSTROM pointed out that ‘‘ . . . it does not help matters by assuming dominance as a necessity in explaining the numerous facts of heterosis and prepotency, and then conveniently discarding dominance for most other forms of quantitative inheritance” and that “ . . . the mere fact that quantitative character data seem to fit a logarithmic curve does not necessarily rule out dominance.” Perhaps neither scheme of gene effects will turn out ultimately to be strictly applicable. It seems likely, on the whole, that the genes determin-

Abstract: ECAUSE, as a rule, lethal genotypes have theireffect during emB bryogeny, where the tempo of development and the magnitude of the structural changes are most marked, they are particularly useful in investigating the role of the genes in development. Furthermore, a study of early-acting lethals offers the possibility of increasing our knowledge of the normal embryology of forms about which little is known at present. Investigations of the nature of lethal disturbances have involved two questions: I) whether the effect can be primarily ascribed to a single structure or group of structures which, because of their pathological condition, prevent further development, or; 2) whether the effect appears to be of a general character, expressed as a disturbance of the dynamics of development which may lead to malformations. The study reported below deals with a deficiency of the X chromosome in Drosophila melanogaster which is lethal when hemizygous. This lethal is interesting because it terminates development a t the very end of the egg stage, thus affording an opportunity of studying organs and anlage which are already well differentiated. Since the normal animal at this stage has not been described in any detail in the literature, an account of the developmental phenomena, and of the anatomy of the larva just prior to hatching has been included for comparison with the lethal embryos.

Abstract: ROSOPHILA algonquin, described by STURTEVANT and DOBZHAND SKY (1936b), belongs to the a$nis group of the genus Drosophila. It was originally found in a few localities in the northeastern United States, but it has recently appeared in a collection taken as far southwest as central Texas. Figure I shows the known distribution of the species. It is the purpose of this paper to give an account of the structure of the chromosomes of Drosophila algonquin and to describe the nature and distribution of variation in gene arrangement within them.

Abstract: YTOLOGICAL analysis (LINDEGREN and RUMANN, in press) has C shown that Neurospora crassa probably contains nine chromosomes. These chromosomes were found to contain respectively, 29, 18, 13, 9, 5 , 3, 3, 2, and I chromomeres; but since they were not completely uncoiled, the number of ultimate chromomeres is probably at least twice as great. They are certainly the smallest chromosomes in which crossing over has ever been analyzed. The sex chromosome in Drosophila, in which comparable studies have been made, contains at least twenty times more chromomeres. In Neurospora, one linkage group containing six loci has already been established (LINDEGREN 1936). If mutations occur at random, about 35 percent of the mutants should be found in the first chromosome and it seems probable that the sex chromosome, which is the longest genetically, corresponds to the longest cytological chromosome. The present paper reports a second linkage group containing four loci. The second longest chromosome contains 22 percent of the chromomeres and probably contains the genes of this second linkage group. About half of the genes should be distributed among seven other linkage groups and many other mutants which have not yet been mapped are being carried in stock. None of these has been found to be linked in those tests which were made. All the mutants used in these studies appeared spontaneously.

Abstract: LARGE proportion of the X chromosome deficiencies maintained A in stock at this laboratory are balanced over In(~)dl-qg, y Hw. When such deficiencies were examined cytologically, it was frequently noticed, especially when the chromosomes were unpaired, that there was some departure from the normal salivary gland chromosome banding of the tip region of the X carrying Hw. Since such material was heterozygous for Hw, which is known to be genetically close to this free or left end of X, it seemed logical to investigate whether the presence of Hw might account for the abnormality observed. Evidence obtained later from duplications for the left end of X gave further support to this theory. Flies carrying duplications obtained from the translocation T(I .4)w 258-18 (DEMXREC and SLIZYNSKA 1937) were phenotypically Hairy wing. This finding suggested that the expression of Hairy wing was due in itself to a duplication for some portion of the X chromosome close to the tip and consequently experiments were planned to determine the presence of such a duplication cytologically and to test its behavior genetically. Following are descriptions of mutants and aberrations which were used in this work. These are adapted from descriptions prepared by C. B. BRIDGES for Drosophila Information Service, No. 9. The mutant character Hairy wing (Hw) was found by C. B. BRIDGES in ~ 9 2 3 as a spontaneous mutation in a y cv tf stock. It has not been possible to separate it by crossing over from y , placing its locus, therefore, at 0.0 k. Males carrying Hw show extra bristles along the wing veins, on the head, affecting especially the occipitals, and on the thorax. Extra hairs also occur on the back of the head and on the pleurae. Females heterozygous for Hw show some extra bristles especially on veins; females homozygous for Hw exhibit a more extreme character than the males. They are not lethal, but their viability is reduced to 80 percent. The rank accorded the character as based on viability and ease of classification is I. The mutant achaete (ac) was found in 1916 by WEINSTEIN (1918) as a spontaneous change in the yellow stock. DUBININ referred to it as scll. It has not been possible to separate it from y, but cytological studies place its locus between y and sc, thus o.o+. On homozygous flies the posterior dorsocentrals are missing, while the anterior dorsocentrals are rarely affected; hairs are usually fewer in the neighborhood of the posterior dorso-

Abstract: Pattern of black and yellow The tortoise shell pattern consists of yellow hairs sprinkled lightly among black hairs in a few irregular, asymmetrical regions over the body. This is the typical pattern of family D, a highly inbred strain which never shows white. Occasionally a foot has a small area of segregated yellow at the tip. Large areas often appear to be solid black. The tricolor pattern of black, yellow, and white, was a feature of the earliest scientific description of the guinea pig. According to CUVIER this variety was described by ALDROVANDUS about 1550 (CASTLE 1912). Compared with the tortoise shell, the tricolor has a tendency to greater segregation of black and yellow hairs (WRIGHT 1917), giving typically i n addition to some brindling clear areas of black, yellow, and white. The individual irregularity of the black-yellow pattern is even greater than for the color-white pattern. In 1916 IBSEN proposed the symbol e p (partial extension of black) for the gene determining the tortoise shell pattern. Later (1919) he reported on the inheritance of the three alleles a t this locus, E (self black) dominant over e p and e (self yellow), and e p dominant over e. The question of dominance in multiple allelic series is interesting and a quantititve study has been one of the objects in the present investigation. No statistical analysis of the array of. modifiers of this pattern has been made but the existence of such modifiers will be shown by differences in average number of yellow hairs in certain experiments.

Abstract: ETAILED analyses of populations containing natural hybrids have D been reported recently. ANDERSON (1936) has suggested a method for expressing quantitatively the extent of hybridity of a population and for comparing various populations, and this method has been applied to various genera such as Tradescantia (ANDERSON 1936) , Solidago (GOODWIN 1937), and Iris (RILEY 1938, 1939) The present paper reports a morphological and cytological study of a population of Tradescantia growing along a railroad right-of-way about fifteen miles east of the center of New Orleans, Louisiana. This population was more complex than most of the populations of that genus reported by ANDERSON and HUBRICHT (1938) for i t involved three species of which two were tetraploids and the third a diploid.

Abstract: HE “anemic” mutation appeared in the Cornell colony of albino rats T which originated from the Osborn and Mendel stock a t the Connecticut Agricultural Experiment Station. Since 1919 the Cornell colony has been a closed one, but inbreeding has not been intense. The rats are maintained on an adequate mixed diet (a commercial calf meal) which is supplemented a t least once a week with cod liver oil to the extent of three percent of the diet (MAYNARD 1930). The anemia appears spontaneously in the young rats and acts as a complete lethal, since all of the affected animals die, usually within the first two weeks of life. When first observed by the authors the gene was so widespread in the colony that it was impossible to trace it back to any one or two individuals in which it may have first occurred. That the mutation occurred in the Cornell colony is supported by the fact that no anemic animals have been noted in the Osborn and Mendel colony (private communication). CREW and KON (1933) found a monogenic autosomal lethal in the rat which first manifested itself a t about the 9-12th day of life when the young rats began to lose weight. They died usually within five days from inanition. The underlying cause of this failure could not be determined, but the authors stated that neither an anemia nor a physiological leucocytosis was present. G R ~ E B E R G (1938), in describing another simple recessive autosomal lethal in the rat, says, “The most fundamental disturbance so far discovered is an anomaly of the cartilage; this simple mechanism affects several structures of the body in a similar way. Hyperplasia of the’ribs and of the cartilage rings in the trachea thus produced leads secondarily to the development of an emphysema of the lungs, and the animals ultimately die from more or less remote consequences of this emphysema.” The time of death of these rats varied from 4-39 days of age. GUNN’S (1937, 1938) case of acholuric jaundice in the rat is another example of a hereditary physiological upset. This is due to an incompletely recessive autosomal gene, the heterozygotes showing some of the characteristic symptoms of the variation, such as increased red cell fragility and reticulocytosis. This mutation is not incompatible with life, for the affected