^^^^^^^^ff ^m ' ^ ^^^^^^■P^tKH f^^^^^^^mi-M.^iu'j < I^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^IBt z fj X ^^^^■^^^^^^^^^^Bt|I|U ! i ®Ijp i. 1. 'Ml library Nortlj (Earolina ^tat? Mmueraitg C25 S006 13992 U THIS BOOK IS DUE ON THE DATE INDICATED BELOW AND IS SUB- JECT TO AN OVERDUE FINE AS POSTED AT THE CIRCULATION DESK. UEC 2 1 1983 MAR - 6 «Jb UAN 3 1995 DEC 3 ^«» my \\^\m V. 50M/2-78 l^orth CaroWifvSLate Library Raleigh CONTEIBUTIONS TO THE GENETICS OF DROSOPHILA MELANOGASTER, I. THE ORIGIN OF GYNANDROMORPHS. By T. H. Morgan and C. B. Bridges. II. THE SECOND CHROMOSOME GROUP OF MUTANT CHARACTERS. By C. B. Bridges and T. H. Morgan. III. INHERITED LINKAGE VARIATIONS IN THE SECOND CHROMOSOME. By a. H. Sturtevant. IV. A DEMONSTRATION OF GENES MODIFYING THE CHARACTER "NOTCH." By T. H. Morgan. J C 4, * ^ , .. » • . -> I .1 ""s * , , > ) > 1 , ) ) ' 1 Published by the Carnegie Institution of Washington Washington, 1919 CARNEGIE INSTITUTION OF WASHINGTON Publication No. 278 Kx L K K « C C 4 1 C t t 1 « * % c t ^ c C t ( 4 (. C c PRESS OF GIBSON BROS, INC. WASHINGTON, D. C. CONTENTS. I. The Origin of Gynandromorphs. By T. H. Morgan and C. R. Bridge; PAGE. S 1 Frequency of Occurrence of Gynandromorphs Relative J^equency^ of Elimination of the Matcrnai' and' Paternal '" Sex Distribution of Segmentation" Nuclei 'as deduced 'from' Distribution of'the ^^ Characters of Gynandromorphs v> Starting as a Male vs. Starting as a Female ,^ Cytological Evidence of Chromosomal Elimination.. \\ Earlier Hypotheses to explain Gynandromorphs. ... \t The Origin of the Germ-cells in FUes ^^ Courtship of Gynandromorphs o Phototropism in Mosaics with one White and one Red Eye 9? Sex-limited Mosaics " ^'^ Somatic Mosaics _\ '^^ Somatic Mutation ^^ Mosaics in Plants ^'^ Classification and description of Gynandromorphs oi Drosophila 11 Gynandromorphs approximately bilateral ^J Gynandromorphs mainly female ^f Gynandromorphs mainly male y. ^ ^ Gynandromorphs roughly "fore-and-aft" ^ Gynandromorphs produced by XX Y females. ... „ Gynandromorphs of complex type [ \ Jt Special Cases ^^ Gynandromorphs with incomplete data ^I Drosophila Gynandromophs previously published 70 Gynandromorphs and Mosaics in Bees If Gynandromorphs in Lepidoptera ot Other Insects «. Spiders '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'..'. 94 Crustacea „_ Molluscs ■''.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'..'. q? Echinoderms no Vertebrates r»Q Fishes y^y^y.'.'.'.'.'.'.'.'.'.'.'.'.'..'. it Amphibia qo Reptiles . ^, Birds yyyyyyy.y:::::::::::.: Z Mammals — Man -.f^f. Is Cancer a Somatic Mosaic? ' .' j"^ Is the Freemartin a Gynandromorph? 1 JJn Summary p'' Literature Cited JP 116 II. The Second Chromosome Group of Mutant Characters. By C. B. Bridges and T. H. Morgan . „„ Introduction " " ' |^^ Chronological hst of the II Chromosome Mutations 1 2fi Map of Chromosome II ,0^ Speck ;:;;;;;; 127 Ohve J28 Truncate J^J Truncate Lethal ti^ Snub .y.'.''.'.y.'.'''.'.'.'.'.'.'.'.'.'.'.'.'.'.'.[ HO Truncate Intensification by Cut 143 III IV CONTENTS. PAGE. II. The Second Chromosome Group of Mutant Characters — continued. Black 144 Balloon .' 148 Vestigial 150 Blistered 155 The Semi-Dominance of Blistered — Free-Vein 158 Jaunty ■. 160 A Mutating Period for Jaunty 161 Curved 164 Purple 169 The Differentiation of Purple by Vermilion — Disproportional Modification . 170 No Crossing Over in the Male 174 The Inviability of Vestigial — Prematuration, Repugnance, Lethals 177 The Purple " Epidemic"—" Mutating Periods" 178 Balanced Inviability, Complementary Crosses 181 The Variation of Crossing Over with Age 183 Coincidence 188 The Relation between Coincidence and Map Distance 188 Special Problems Involving Purple — Age- Variations, Coincidence, Tempera- ture-Variations, Cross-Over Mutations, Progeny Test for Crossing-Over 193 Strap 200 Arc 202 Gap 208 Antlered 211 Dachs 216 Streak 222 Dominance and Lethal Effect of Streak, Parallel to Yellow Mouse 223 Comma 228 Morula 230 Female Sterility of Morula 230 Apterous • 236 Cm and Ciir 239 Cream 11 239 Trefoil 244 Cream b 245 Pinkish 247 The Double-Mating Method 248 Plexus 251 Limited 254 Confluent 255 Confluent Virilis 257 Fringed 257 Star 259 Lethal Nature of the Homozygous Star 260 Crossing Over in the Male 263 Nick 273 Vestigial-Nick Compound 275 Dachs-Lethal 277 Dachs-Deficiency? 278 Balanced Lethals 279 Squat 283 Lethal Ila 286 Telescope 291 Second Chromosome Modifiers for Dichaite Bristle Number 293 Dachsoid 294 The Construction of the Map of the Second Chromosome 297 Summary of Available Data on Crossing Over in the Second Chromosome 298 Constructional Map 302 Working and Valuation Map 303 Bibliography 304 CONTENTS. V PAOE. III. Inherited Linkage Variations in the Second Chromosome. By A. 11. Sturtevant. 305 Introduction 307 " Nova Scotia" Chromosome 307 Tests of Cross-Overs 312 Right-hand end of Nova Scotia Chromosome (C// r) 313 Left-hand end of Nova Scotia Chromosome (C// i) 316 Homozygous Cii r 319 With Cm 319 Without Cn 321 No Tests of Homozygous Cn l 322 Tests Showing No Crossing-Over in Males 322 Constitution of the Nova Scotia Stock 322 Another Second-Chromosome Linkage Variation 324 Comparison with Results obtained from Cm 325 Discussion 327 Summary 330 Appendix 331 Literature Cited 341 IV. A Demonstration of Genes Modifying the Character "Notch." By T. H. Morgan 343 Variation of Notch 346 The Problem 347 Condition of Stock before Selection 348 Selection of Females having Notch in one Wing only 349 Selection of Somatically Normal Winged Females that are Genetically Notched Females 350 Duplicate Selection Experiment 355 Localization of the Gene for Notch 358 The Indentification of the Modifying Genes 361 Short Notch 364 First Test 366 Second Test 367 Thh-d Test 368 Fourth Test (for fourth-chromosome modifiers) 369 Recombination of Bent and Short Notch 370 , Crosses between Short Notch and Other Stocks 371 Short Notch by Star Dichsete 372 Short Notch by Eosin Ruby Forked 372 Classification of Types of Notch 376 Aberrant Notch Wings 379 Deformed Eyes 379 Little Eyes 381 High Sex-ratios Caused by Lethals 381 Other Characters that Look Something Like Notch 382 Gynandromorph; Notch Eosin Ruby 384 Summary 387 I. THE OBIGIN OF GYNANDEOMORPHS. By T. H. Morgan and C. B. Bridges. With four plates and seventy text-figures. I. THE ORIGIN OF GYMNDROMORPHS. By T. H, Morgan and C. B. Bridges. INTRODUCTION AND GENERAL DISCUSSION. The sharp distinction into two kinds of individuals, males and females, characteristic of so many animals, is occasionally done away with when an individual appears that bears the structures peculiar to the male in some parts and to the female in other parts of the body. Such an individual may show not only the secondary sexual differences (either sex-limited or sex-linked) of male and female, but gonads and genitalia of both kinds as well. We speak of these as gynandromorphs. The union of the two sexes in a single individual shows how far the characteristics normally associated with one sex alone are compatible with the presence in another part of the same body of somatic structures and reproductive organs of the opposite sex. In a word, how far each is independent of sex hormones. But the chief importance of these rare combinations lies in the opportunity they furnish for analysis of the changes in the hereditary mechanism of sex determination that makes such combinations possible. This evidence is chiefly derived from gynandromorphs that are also hybrids. Such individuals may combine not only male and female sex differences, but the character- istic racial differences as well. Whether gynandromorphs arise more frequently in hybrids or whether it is only that their detection is easier under such circumstances will be discussed later. The occurrence of hybrid gynandromorphs offers at any rate a unique opportunity to discover the method of origin of such kinds of individuals. In hybrid gynandromorphs the differences that are shown may be due to genes carried by the sex chromosomes. Most of the gynandro- morphs of Drosophila belong to this category. In many cases, how- ever, especially in other insects, it is not known whether the differences shown by the hybrid gynandromorph are due to the sex chromosomes or to other chromosomes, either because the ancestry of the gynandro- morph is unknown or because the method of inheritance of the gene is unknown. There are, however, some very rare cases in Drosophila in which the characters involved are probably autosomal and the individual, while showing its dual parentage in different parts of the body, is not a sex-mosaic. It may be convenient to designate such types as mosaics, while the sex-mosaics may be designated by the more special term gynandromorphs. In our work on Drosophila melanogaster (ampelophila) a large number of gynandromorphs and mosaics have appeared, and since the first THE ORIGIN OF GYNANDROMORPHS. description of a few of them was published we have continued to keep records of their occurrence. Others, too, working with our mutant types have found them, and a few have been described by Dexter, Duncan, and Hyde. We soon reahzed that they occurred with suffi- cient frequency to make it possible to devise experiments of a sort to furnish the long-sought criterion as to the most common method of their occurrence. It is this evidence on which we wish now to lay chief emphasis. The ordinary gynandromorph is an animal that is male on one side of the body and female on the other. The reproductive organs, gonads, and ducts may or, in bees at least, may not show a corre- sponding difference. A typical case of a gynandromorph that is bilateral, at least superficially, is represented in plate 1, figure 1. For a long time it has been recognized that bilateral gynandromorphism is only one kind of abnormal distribution of the sex characters; even in the classical case of the Eugster bees (see p. 74) other distributions of the characters were recorded. In the fly represented in plate 3, fig- ure 2, the upper part of the abdomen is female, but the lower side of the abdomen, notably the external genitalia, are male. In the individual represented in plate 3, figure 5, the left anterior side of the head is male, the right fe- male, while the left posterior parts of the body are female, the right male. Other cases will be described later in which even more irregular and complex distributions of male and female parts exist. Before discussing these and other cases in detail, it may be well to give three of the most recent interpreta- tions of gynandromorphism resting on a chromosomal basis and the criteria by which the validity of each has been tested. In 1888 Boveri suggested that on rare occasions a spermatozoon, on entering the egg, might be delayed in its penetration to the vicinity of the egg-nucleus, and the latter might meanwhile have begun to divide, so that the sperm-nucleus came to unite with only one of its halves. In consequence, two kinds of nuclei would be produced in the embryo (text fig. 1 a) . The nuclei that come from the sperm plus the half egg-nucleus would be diploid. If, as in the bee, one nucleus stands for the male and two for the female, it follows in such cases that all those parts of the body whose nuclei are derived from the Text-figure 1. THE ORIGIN OF GYNANDROMORPHS. 5 single (haploid) nucleus would be male, all those from the double (diploid) would be female. Moreover, if the two differ in one or more characters, the male parts of the gynandromorph should be expected to be like the mother, i. e., maternal, and the female parts should be paternal if the paternal characters involved are dominant. The pos- sibiHty of testing Boveri's hypothesis was pointed out by one of us (Morgan) in 1905, and a test case was apparently furnished by a hybrid gynandromorph of the silkworm moth described by Toyama. The result was not in harmony with Boveri's hypothesis, but since the relation of one or of two nuclei to sex was not then known for moths, the case is not decisive, as will be shown more at length later. On the other hand, Boveri's discovery of some preserved specimens of the original Eugster gynandromorph bees and his analysis of their hybrid characters seemed to show that the condition of these bees was com- patible with his theory. This evidence will also be taken up more fully later. We may anticipate our account of hybrid gynandromorphs of Drosophila and state that they furnish direct evidence against Boveri's hypothesis, for these flies at least. In 1905 Morgan suggested an alternative hypothesis based on the fact that more than one spermatozoon had been found to enter the bee's eggs. Should one only of these sperm-nuclei unite with the egg-nucleus, the combination would give rise to the diploid cells of the embryo, while if a second (or a third, etc.) sperm-nucleus should develop it would give rise to haploid cells in the rest of the embryo (fig. 1 b) . On this view the haploid cells should be paternal and pro- duce male parts, and the diploid cells maternal and produce female parts, which is exactly the reverse relation in regard to parental origin of the male and female parts from that expected on Boveri's hypothesis. A decision as to which view is correct might be reached in any special case in which sex-linked characters enter from the paternal and maternal sides. As will be shown later, some of the evidence from the Drosophila gynandromorphs is incompatible with this hypothesis of Morgan. A third hypothesis that grew out of the work done in this labora- tory was published in 1914 by Morgan, based on evidence from the Drosophila cases. On this view the gynandromorphs are due to an elimination of one of X chromosomes, usually at some early division of the segmentation-nuclei. Rarely, in consequence of a delay in the divi- sion of one of the X chromosomes, one of the daughter-halves fails to reach its pole and is lost in the mid-plate or in the cell-wall (fig. 1 c). As a result, the embryo comes to carry two kinds of nuclei, one kind containing one X and the other kind two X chromosomes. The critical evidence in favor of this interpretation is found in the presence on both sides of the gynandromorph of other mutant characters whose genes are not in the X chromosomes, but in autosomes. If, for example, 6 THE ORIGIN OF GYNANDROMORPHS. the mother contains a mutant gene in one of her autosomes and the father contains its normal allelomorph, it is expected, on Boveri's view, that the male side of the gynandromorph should show this maternal autosomal character, even though recessive. But on the hypothesis of chromosomal elimination, both sides of the gynandro- morph should show the same autosomal characters. Conversely, if the cross is so arranged that a recessive mutant autosomal gene enters from the father's side, then, on Morgan's earlier view of polyspermic fertilization, the male side of the gynandromorph should show this recessive mutant character; but on the elimination hypothesis both sides should show the same (dominant) autosomal characters. It may now be shown by critical examples that the hypothesis of chromo- somal elimination will cover nearly all of the cases of Drosophila, and is therefore preferable to either of the other two, even although in special cases either of these two other ways of producing gynan- dromorphs may be reaUzed. A few additional cases have been found that call for still other interpretations. The critical cases are as follows: A yellow white male was mated to a female pure for the recessive autosomal genes for peach eye- color, spineless body, kidney eye-shape, sooty body-color, and rough eyes. A gynandromorph was found (plate 1, fig. 1) that was male on one side, as shown by his shorter wing, sex-comb on the foreleg, and the shorter bristles characteristic of the male (the body was also slightly bent to the smaller male side), and female on the other side, as shown by the converse characters to those just given. The gynandromorph possesses on both sides all of the characters dominant to the five recessive autosomal factors that came in with the sperma- tozoon. On Boveri's explanation, the male side should have a yellow body-color and a white eye, because their two genes are carried by the maternal nucleus, while the female side should show the normal characters of the wild fly, as is the case. The absence of yellow body-color and white eyes on the male side rules out his explanation. On Morgan's hypothesis of polyspermy, the male side that comes from one or more supernumerary sperms should show the five auto- somal recessive characters brought in by each sperm, which is not the case, and the female side should show the normal characters, as it does. The absence of the five recessive characters on the male side rules out this explanation also. On the theory of chromosomal elimination the gynandromorph started as an ordinary XX female — one X carrying the genes for yellow and for white, the other carrying their normal allelomorphs, viz, genes for gray and for red. Either of these chromosomes might be the one to be eliminated, i. e., at some division either one of the yellow white daughter chromosomes failed to reach one of the daughter cells, or one of the gray red daughter chromo- somes failed. If the former, the male side should get only the gray PLATE 1 _,^~- \ \\ ^f\J \^' ***i», ^•a. /■•^ / ■\ .^ '\ / \ ~>M<:" / V. ^ li. ;\I. Wallace I'inx GYNANDROMORPHS OF DROSOPHILA THE ORIGIN OF GYNANDROMORPHS. 1. red chromosome, and show the corresponding characters, which in fact it does. If the other chromosome had lost one of its halves at the critical division, the male side should be yellow white, which is not the case. Evidently, then, it must have been a yellow white daughter chromosome that was lost in this case. In regard to the five autosomal characters, it is clear that since both male and female sides show all the dominant characters, both sides of the body received the autosome that bears their genes. This hypothesis thus covers the facts in the case. Sections of the abdomen showed abnormal gonads that appeared to be testes. Another gynandromorph is drawn in plate 1, figure 2. It, too, came from this same cross of a yellow white male by a female of a race with the same five recessive characters. It is not a bilateral Text-figure 2. gynandromorph, but more nearly an anterior-posterior combination. The abdomen is male, and since the forelegs bear no sex-combs, some at least of the anterior end is female. One wing is male; at least it is shorter than the one on the opposite side, which is presumably female. As in the last case, the fly shows only the characteristics belonging to the normal allelomorphs of the five recessive autosomal factors. The analysis here is the same as above. Another gynandromorph, drawn in text-figure 2, arose from a cross between a male that was heterozygous for the two dominant autosomal genes for star eyes and for dichaete bristles and a female that was notch 8 THE ORIGIN OF GYNANDROMORPHS. (* 'short" type) . The mother had one sex chromosome with the dominant gene for notch and another sex chromosome that had the normal allelo- morph of notch and also a gene for eosin eye-color. The gynandromorph was male on one side, with an eosin eye (with a red fleck in it), a sex- comb, and a short wing on that side, and female on the other side with a red eye, no sex-comb, and a longer wing. The genitalia were male. The gynandromorph arose by the fertilization of an egg containing the sex chromosome bearing the eosin eye-color (because had the other maternal X chromosome been present one of the wings, or both, would have shown the notch character). In this case it was the X chromo- some from the father that was .eliminated, since the male side shows the eosin eye-color of the maternal sex chromosome. Boveri's ex- planation will not fit this case, even though the male side shows a miaternal character, viz, eosin eye, because that side is dichaete, hence contains dominant factors from the paternal autosome. Morgan's hypothesis of polyspermy will not fit this case, for the male side should have red instead of eosin eye-color, since red was brought in by the sperm. On the hypothesis of elimination, it is apparent that one of the daughter halves of the normal X chromosome was lost ; the cells of both sides got the regular autosomal groups, for dichsete came from the father. The father was heterogyzous for star, and it must have been one of his gametes without star, but with dichsete, that fertilized the egg. Here again neither of the earlier explanations fits the case, but the third hypothesis covers it. Another gynandromorph was described in ''Mosaics and Gynandro- morphs in Drosophila" in 1914. It was the first case discovered in which the presence of an autosomal factor made it possible to decide which of the three explanations was the correct one. A yellow white female was crossed to a male that carried a recessive autosomal gene for ebony body-color. The gynandromorph was preponderantly male on one side and female on the other. Both eyes were red and the body-color was gray (or possibly heterozygous ebony) on both sides. Here Boveri's explanation fails, because the male side should have been entirely maternal, therefore yellow and white; and Morgan's earlier explanation fails, because the male side was not ebony. On the elimination hypothesis a maternal yellow white daughter chromo- some was lost ; hence both sides had red eyes and not yellow body-color, and both sides received the same normal autosomes. This cross, in which a yellow white female was mated to an ebony male, was carried out extensively (January to May 1914) and 6 more gynandro- morphs were found. However, in order to discriminate between partial fertilization and polyspermy on the one hand and elimination on the other only those cases are diagnostic in which the male parts come from the father and show at the same time autosomal parts from the mother. THE ORIGIN OF GYNANDROMORPHS. 9 Another gynandromorph (obtained by Sturtevant), text-figure 3, came from a mother that had in one second chromosome the genes for C„i and for curved, and in the other the genes for black and for vestigial. She may have had a third chromosome gene for crossing- over. The father was homozygous for black, purple, curved, plexus, speck, all in the second chromosome. Brothers and sisters were as expected; the black curved crossing over was 28 per cent. The fly was black and showed no trace of purple, vestigial, curved, plexus, or speck. It was male on the left side, female on the right, except for head bristles. The genitalia were male. The fly was sterile. Unless the egg were a double cross-over for black vestigial curved, which is unlikely, it contained a black vestigial bearing chromosome. The sperm contained the five sec- ond-chromosome genes. Since the male parts showed none of these sec- ond-chromosome char- acters, except black, although all the rest ex- cept purple might have been visible, it is highly probable that the male parts contained both sec- ond-chromosomes. The result shows at least that the theory of chromo- some elimination is a more probable explana- tion than partial ferti- lization or multiple ferti- lization, and the result would be conclusive if the possibility of double crossing-over were rejected. Another case (found by Sturtevant, 4079 C, Oct. 31, 1917) occurred in a cross betweem a male with a normal X chromosome and pure for the second-chromosomal genes for black, purple, and curved, and a forked female that was heterozygous for the second-chromosomal genes for black, purple, and curved. The gynandromorph (plate 1, fig. 3) had a short wing on the left side, but the left foreleg was not male. The abdomen had the male banding and genitalia and contained two testes. No forked bristles were found in any part of the body. Elim- ination of one of the forked-bearing maternal X chromosomes left the wild-type X chromosomes to determine the character of the male parts. Text-figure 3. 10 THE ORIGIN OF GYNANDROMORPHS. The gynandromorph must have received the normal second chromo- some from its mother (since normal autosomal characters only ap- peared) and a second chromosome from its father with the three recessive genes. Since neither male nor female parts show these recessive genes, two second chromosomes must have been present in all the nuclei, both in the male and in the female parts. FREQUENCY OF OCCURRENCE OF GYNANDROMORPHS. In general, we have no record of the frequency of the occurrence of gynandromorphs. They are found from week to week, their number being roughly in proportion to the number of flies passing under observation, and also in proportion to the care with which the flies are scrutinized in detail. On four occasions, however, the frequency of their appearance was recorded. In the first case (in 1914) a cross, involving yellow flies, white-eyed and eosin-eyed flies, and wild-type flies, seemed to give gynandromorphs more often than usual. It is to be noticed that the striking color differences of eye and body in this combination would, as a rule, make it easy to detect hybrid gynandromorphs, and their frequency may have been due to this fact. In all 32 gynandromorphs were found in a total of 42,409 flies, or 1 in 1,325. Duncan, in 1915, made a careful examination of hybrid flies and found 3 gynandromorphs in a total of 16,637 flies, or 1 in 5,500. All flies were so thoroughly scrutinized that probably most of the gynan- dromorphs that occurred were found. The third set of observations was made on material that was chosen because, in addition to sex-linked factors, autosomal genes were present, which should give an answer to the three contrasted hypotheses de- scribed in the preceding pages. In all, 2 gynandromorphs were found in a total of 4,979 flies. A fourth record made by Sturtevant also involved autosomal as well as sex-linked characters. Forked females were mated to males with normal bristles. The female was heterozygous for the second- chromosome genes, black, purple, curved; the male homozygous for the same genes; 3 gynandromorphs were found in about 24,000 offspring. Taking all these results together, the observed ratio is 1 gynandro- morph in 2,200 flies. Whenever the chromosomal elimination occurs at an early stage in development, or when the color or structural difference involved is striking, the gynandromorph is more likely to be found than when the contrary conditions are present. If elimination occurs late in develop- ment the region affected may be so small as to escape detection. It seems probable, therefore, that such irregularities may be more frequent than the figures given above indicate. THE ORIGIN OF GYNANDROMORPHS. 11 It is a curious fact that practically all of the mosaics of Drosophila involve the sex chromosomes. It is true that the differences in the sexes are so marked that individuals partly male, partly female, could easily be detected on this basis alone. On the other hand, the mutant characters that are sex-linked are not more striking than are those of autosomal mutants. The almost complete absence of the latter kind of mosaics in our cultures shows very positively that elimination is very infrequent in these chromosomes, or, if it occurs, that an individual or part with only one autosome is less likely to survive than an individual with one X chromosome. Until this question is settled it can not safely be concluded that the sex chromosomes suffer elimination more than do the autosomes. The fact that autosomal non-disjunction has not yet been observed in Drosophila, though looked for, lends support to the view that variations in autosomal number are either rare or are fatal. RELATIVE FREQUENCY OF ELIMINATION OF THE MATERNAL AND PATERNAL SEX CHROMOSOME. It might have been supposed a priori that delay in the unraveling of the chromosomes of the sperm might be the most frequent cause of the elimination of chromosomes. As a matter of fact, the evidence shows clearly that the maternal X is as likely to be eliminated as the paternal. For example, we find on looking through our records that in 15 cases the maternal X chromosome and in 15 cases the paternal chromosome must have been the one eliminated. There were 16 cases in which from the nature of the cross or of the result it could not be determined which one was eliminated. In the above estimation we also have left out of account all cases that were entirely male, or for which special explanations are called for. There can then be no doubt but that eUmination is somehow connected with the nature of the X chromosomes themselves, such as slowness in dividing or in reaching the poles of the spindle, and that elimination is not due to delay in the development of either pronucleus. An examination of the gonads in Drosophila gynandromorphs has shown in every case that the two gonads are the same, i. e., both are ovaries or both are testes. Even in bilateral types the two gonads are alike. Duncan found this true for the few cases that he sectioned. This number was, however, insufficient to establish the rule, but we can now add about 20 other cases to the list. There can remain no doubt that the gonads are alike, regardless of the way in which the male and female parts are distributed on the surface. The results are in accord with the early formation of the germ-cells in Diptera and probably mc^n that both gonads are derived from one and the same cleavage nucleus. 12 THE ORIGIN OF GYNANDROMORPHS. DISTRIBUTION OF SEGMENTATION NUCLEI AS DEDUCED FROM DIS- TRIBUTION OF THE CHARACTERS OF GYNANDROMORPHS. If the first division of the segmentation nucleus corresponds with the right and left sides of the embryo, and if chromosomal eUmina- tion is more common at this time or more easily detected, we should expect most gynandromorphs to be roughly bilateral. We have found that this is the most frequent type. If the first division were in the antero-posterior direction and elimination were frequent at this time, we should expect to find some gynandromorphs with the anterior end of one sex and the posterior end of the other sex. This type also is fairly frequent. If the first division were dorso-ventral we might expect correspond- ing gynandromorphs, but, although more difficult to detect, they appear almost never to be of this kind. If the second division were a time of elimination we would expect quadrants instead of halves. Such cases are known. The striking fact about the gynandromorphs is that large regions of the body are involved. Granting that later differences would be less easily detected, in certain organs at least, the results are so em- phatically in favor of large parts of the body being involved that we think it highly probable that the elimination is most frequent in the first division. The difficulty of reaching a decision is greatly increased when it is recalled that from the ventral plate of the embryo the serosa is formed by a folding upward of the sides of the plate. How much of the ventral ectoderm is carried in this way to the dorsal surface is not known. Should it replace the dorsal covering derived from the segmentation nuclei (that goes then into the serosa which is later thrown off), the results for ectodermal organs are restricted to the regions on each side of the ventral plate. The mesoderm also grows from the ventral to the dorsal surface, and presumably mesodermal dorsal structures have come from ventral material. A further complication arises in connection with the imaginal plates out of which many adult organs are produced. Unless the exact origin of their cells is known, it is not possible to safely conclude at what time the early elimination takes place. STARTING AS A MALE VERSUS STARTING AS A FEMALE. The evidence recorded in the preceding pages is analyzed on the basis that the gynandromorph starts as an XX individual, or female, and that the male parts arise by the elimination of an X from one of the cells. The evidence from hybrid combinations shows very clearly that practically all of our gynandromorphs have started as XX individuals, as 19 are more female, 14 nearly equal, 6 more male. THE ORIGIN OF GYNANDROMORPHS. 13 There are, however, other theoretical possibiHties that should be noticed, for it is possible that gynandromorphs may sometimes arise in other ways. In fact, one or two of those we describe may he ex- plained in the following way : An X egg fertilized by a Y sperm (a regular male), might later become partly female, i. e., gynandromon)h, through somatic non-disjunction, both daughter X's remaining in the same cell at some early embryonic division. Parts descended from the XXY cell are female; the other (Y) cell would presumably die. If such a process occurred at the first division and all of the yolk was later occu- pied by the viable XXY cells, the embryo would become entirely female, although containing only sex-linked genes from the mother, and might be mistaken for a case of 'primary non-disjunction.' A non-disjunctionally produced egg containing a Y chromosome or an egg without a sex chromosome fertilized by an X sperm might also, starting as a male, produce a purely paternal female or female parts (mosaic) through somatic non-disjunction. If non-disjunction occurred at a late division a proportionately smaller part of female tissue would be formed and the regular male cells formed earlier would give male parts — i. e., the individual might be more male than female. There are no cases where these explanations only will apply, but a few cases accounted for by chromosome elimination may be also explained in one or the other of these ways, viz, that the gj-^nandro- morph started as a male. CYTOLOGICAL EVIDENCE OF CHROMOSOMAL ELIMINATION. The most important case of chromosomal elimination involving one of the sex chromosomes, and therefore most like the case of gynandromorphism in Drosophila, has been described in Ascaris (Rhabditis) nigrovenosus by Boveri and by Schleip. In this nematode there is a hermaphroditic generation that lives in the lungs of the frog. Eggs and sperm are produced at the same time in the her- maphroditic gonad. The full number of chromosomes is the same in the earlj'- oogonia and spermatogonia. This number is reduced to half in the egg and also in the sperm at the reduction division, but while all the eggs are alike, there are two kinds of spermatozoa, one containing one less chromosome than the other. This loss of one of the chromosomes in one-half of the sperm-cells is apparently brought about as a regular process by the failure at reduction of one member of the paired sex chromosomes to reach the pole. It is caught at the division plane or else remains near that plane and disappears. This process differs however, from what we suppose to occur in eliminating a sex chromosome in Drosophila when a gynandromorph is produced in that an undi\'ided X is lost. Whether in Ascaris this process occurs in all the cells at a given division or is somewhat irregular is not certain, and can only be determined by a fuller knowledge of the ratio of males 14 THE ORIGIN OF GYNANDROMORPHS. to females that result. Boveri thought, from the evidence obtained, that the loss of one chromosome at this time is a constant phenomenon. If so, it differs in this regard from the rare occurrence of eUmination in Drosophila. In the group of aphids and phylloxerans a process occurs that has at least a certain analogy to elimination. When the male-producing egg, which is smaller (in the latter group) than the female-producing egg, throws off its single polar body, one sex chromosome is eliminated from the egg, although the autosomes divide equationally at this time. This elimination is not due to loss of a daughter chromosome, because it is preceded by a sort of synaptic union and disjunction of the chromosome in question. Here the lagging of one whole chromosome in the middle part of the spindle, and its failure to reach the outer pole in time to become incorporated in the nucleus of the polar body, furnishes a certain resemblance, at least, to the elimination process. In one species, P. fallax, there are four sex chromosomes, two of which are eliminated from the male-producing egg, as described above. There remain, then, two sex chromosomes in the male. When the sperms are produced these two do not act as mates when the other chromosomes (autosomes) pair and segregate, but both pass together to one pole. The daughter cells that get them become the functional female-producing spermatozoa; the other cell that lacks them de- generates. Here, then, although two sex chromosomes are present, they both pass to one pole. This behavior is quite unlike the results produced by chromosomal elimination. In one of the aphids Morgan found a cyst in which, owing apparently to the failure of the autosomes to pair before segregation, an irregular distribution of the chromosomes took place, including an erratic dis- tribution, somewhat imperfect, it is true, of the sex chromosomes also. This unusual and irregular occurrence might lead to compUca- tion in the distribution of the sex chromosomes in the next generation, if such sperm were to become functional, and furnish a parallel case to the phenomenon of primary non-disjunction that Bridges has described in Drosophila. In Drosophila there takes place on rare occasions an erratic distribu- tion of the sex chromosomes, either in the male or in the female, that has been called primary non-disjunction. Occasionally, both sex chromo- somes are eliminated in the polar body, leaving in the egg the haploid number of chromosomes, but not a sex chromosome. If such an egg is fertilized by a female-producing sperm containing one X chromosome, an XO male results. The male, lacking the characteristic Y chromo- some of the normal male, nevertheless resembles a normal male in all respects, except that he is sterile. Conversely, in other cases, both X chromosomes may remain in the egg. Such an egg does not develop if it is fertilizied by a female-producing sperm giving it three X's, but THE ORIGIN OF GYNANDROMORPHS. 15 if such an egg is fertilized by a male-producing Y-bearing sperm, it produces a female XXY, that is like a normal female in its somatic characters; but such a female, owing to the presence of three sex chromosomes (XXY), gives rise to the phenomenon of secondary' non-disjunction to be described presently. Similarly in the male, primary non-disjunction may take place in the formation of the spermatozoon. If at the reduction division the X and Y chromosomes, that normally pass to opposite poles, should pass to one pole, a spermatozoon would result from one of the daughter cells that contains both an X and a Y, and such a sperm fertilizing an X-bearing egg would give rise to an XXY female that would exhibit secondary non-disjunction. The other daughter cell without X or Y also produces a functional sperm. In these cases of primary non-disjunction an irregular distribution of the sex chromosomes leads to unusual tj-pes of sex-linked inheritance, but not to gynandro- morphism or to mosaics. In secondary non-disjunction, owing to the presence of three sex chromosomes, any two of which may form a pair, there is left one chromosome without a mate. Genetic analysis shows that the un- paired chromosomes, in some cases one of the X's, in others the Y, may either pass out of the egg at maturation or remain in the egg. Aside from this irregularity there is not much in the process that is akin to the kind of chromosomal elimination postulated for gynandro- morphs, since the processes underlying the two phenomena are prob- ably quite different. These cases furnish exceptions in regard to genetic behavior and furnish important evidence bearing on the deter- mination of sex, but do not lead to the kinds of effects seen in the pro- duction of gynandromorphs, except when the non-disjunction occurs at a cleavage stage, as already explained. As stated, Boveri based his hypothesis of gynandromorph produc- tion on an earlier observation that he had made with the sea-urchin eggs. He found that occasionally the egg-nucleus began to divide before the sperm-nucleus had fused with it. In consequence, the sperm-nucleus fertilized, as it were, only one-half of the egg; i. e., it approached one of the two daughter nuclei, and later became incorporated with that one. In consequence, all the nuclei descending from this fusion had the diploid number of chromosomes, while the nuclei descending from the single daughter egg-nucleus had only the haploid number. In the sea-urchin it has not been found possible to raise plutei fo maturity; hence the effect of this partial fertilization on sex could not be determined. Boveri's application of this evidence to gynandromorphs of the bee was purely theoretical, since at that time the genetic evidence, that has since become available, did not exist. At about the same time Herbst carried out some experiments with sea-urchin eggs that enabled him to produce a large number of em- 16 THE ORIGIN OF GYNANDROMORPHS. bryos in which a process similar to that just described took place. The unfertilized eggs were stimulated to parthenogenetic develop- ment by placing them in sea-water containing a little valerianic acid. After a few minutes the eggs were returned to sea-water and sperm added. The sperm-nucleus did not penetrate in many cases until the egg nucleus had begun to divide and then, as in Boveri's case, it often united with one of the daughter nuclei. In neither of the cases is there any elimination of single chromosomes, but in a more general sense the earlier group of paternal chromosomes was dislocated in that it failed to reach its normal destination. The extremely important experiments that Baltzer made with sea- urchin eggs resulted in demonstrable cases of elimination, but here of whole undivided chromosomes. For instance, when the eggs of Strongylocentrotus are fertilized with the sperm of Sphoer echinus, it is found at the first division of the egg that while some of the chromo- somes divide and the halves move to opposite poles, other chromo- somes remain in place, or become scattered irregularly between the two poles of the spindle. They appear later as irregular granules and show signs of degeneration, and although remnants of them may persist for a while, they take no further part in the development. The maternal egg-nucleus contained in this case 18 chromosomes and likewise the paternal sperm-nucleus. Hence, after union and division, 36 chromosomes should go to each pole of the segmentation spindle if all divided. Baltzer found, however, only 21 chromosomes at each pole, which means that 15 chromosomes have failed to behave normally, and it is probable that these are derived from the paternal nucleus. Three chromosomes only of the latter, on this interpreta- tion, take part in the division. In consequence, the nuclei of the embrj'o contain almost exclusively maternal chromosomes, and it is significant that the larvae are largely or entirely maternal in char- acter. It is true that we have no evidence to show at present that the larvae of these sea-urchins differ in only one or more Mendelian factors. It would be very surprising if such were the case, yet the results show at least so great a preponderance of maternal characters that we must infer that the three surviving paternal chromosomes produce no marked difference. The reciprocal cross gave a different result. When the eggs of Sphcerechinus are fertilized by the sperm of Strongylocentrotus, di\asion of all of the chromosomes takes place normally and 36 are found at each pole. The pluteus that develops shows peculiarities of both paternal and maternal types. The difference between the two crosses is probably due to the observed differences in the behavior of the chromosomes. In the first case, the lagging and subsequent degenera- tion of certain chromosomes may be spoken of as a sort of elimination, although the causes that bring it about must be supposed to be of a Raleigh ^ THE ORIGIN OF*^?;fejmBr)MORPHS. 17 different kind from those involved in Drosophila when a half of a single chromosome fails to reach its normal destination, * EARLIER HYPOTHESES TO EXPLAIN GYNANDROMORPHS. Dalla Torre and Friese (1897) and Mehling (1915) have reviewed the earlier attempts to account for gynandromorphs. D()nhofT (1860) suggested that gynandromorph bees arose from eggs with two yolks, one of which was fertilized, the other not; one began to form a worker, the other a drone, both fusing into one individual later. A second interpretation based on Dzierzon's theory was also suggested, viz, that the egg contains the male potentiality, the sperm the female poten- tiality. In fertilized eggs the latter influence usually predominates. In the gynandromorph, one of these influences predominates in one region, the other in other regions. In 1861, Wittenhagen suggested that a queen that produces gynandromorphs has reached a higher stage of fertility which causes male parts to arise even after fertiliza- tion. Menzel (1862) made several guesses, such as that delayed fer- tilization of the egg leads to irregular distribution of the mass of the sperm material with consequent disturbance in the development. Later (1864) he suggested that abnormal organization of the oviducts, leading to delay in passing of the egg, interferes with the sperm, so that the egg no longer has the possibility of producing a complete female, except in certain regions of the body. Von Siebold (1864) thought that insufficient fertihzation is re- sponsible for the appearance of gynandromorphs. He assumed that a definite number of spermatozoa are necessary to produce a female. When from any cause an insufficient number of sperms is present, the egg can not develop a female, or a male, but an intermediate type. According to Cockayne (1915, p. 117), Scopoli (1777) suggested that a gynandromorph of Phalcena pini might have arisen through the fusion of two pupae lying in one cocoon. Donhoff's suggestion (as above) of two yolks in one shell that fused is a somewhat similar view, and Wheeler in 1910 made a like suggestion, viz, that two eggs (fer- tilized?) fused at a very early stage, one a male-producing, the other a female-producing. Such a process will not apply, however, to most of the cases in Drosophila, because the evidence shows that the eggs are normally not of two kinds. The male alone produces two kinds of gametes. The sex-hnked characters in hybrid gynandromorphs show very clearly that the results are not due to the fusion of two eggs, but to a different sort of process. In the bee also it appears that there is only one kind of egg, and that the female sex is determined by the fertilization of the egg; the male comes from the unfertilized egg. On the other hand, there are several cases in Drosophila which can not be explained by simple chromosomal elimination, but which can be explained on the assumption that the egg had two nuclei. Here 18 THE ORIGIN OF GYNANDROMORPHS. the appeal is made to a binucleated egg in order to account for the distribution of the* sex-linked characters, but only indirectly for the sex differences in the gynandromorph. The different sexes in the two parts are due to fertiUzation of the two nuclei by male and female producing sperm respectively. The presence of two nuclei in these eggs is easily explained as due to the fusion of two oogonial cells or else by an oogonial nuclear division without cytoplasmic division. The conditions existing at the completion of the last oogonial division are particularly favorable for such a union, for at this stage from a collection of cells (presumably all aUke) the most favorably situated turns into the egg and the others into nurse-cells very intimately con- nected with the egg-cell. This view, while similar to Wheeler's, puts a different emphasis on the facts, for here the presence in the eggs of two nuclei does not directly account for the different sex of the parts of the gynandromorph (for this difference is due to the two kinds of sperm that have entered), but explains the distribution of the sex- linked characters in the hybrid gynandromorphs. On the other hand, Wheeler's idea is that two eggs in themselves determined as male and female fuse bodily, i. e., side by side, to give rise to male and female parts respectively. His view would be more nearly reahzed in the case of moths where the female is the heterozygous sex, and consequently a binucleated condition can be utilized directly to ex- plain not only the difference of sex in the gynandromorph (one nucleus retaining a Z and the other a W chromosome), but also the autosomal mosaics, as in the cases described by Toyama. Arnold Lang suggested another possibility in 1912, viz, that an egg that had developed parthenogenetically to the stage when the first two nuclei were formed might be fertilized by a female and a male producing sperm, each sperm uniting with one or the other of the two egg-nuclei. As a result one half should be male, the other half female. The hypothesis will not apply, however, to the bee — the forms whose parthenogenetic process of development would seem to best fit such a view — because only one kind of sperm is supposed to be produced. Double nuclei should produce female parts. The explanation will also obviously not apply to such cases in Drosophila as those in which the male half shows maternal recessive factors. De Meijere (1910-11) has offered certain suggestions concerning the origin of gynandromorphs. He starts from the old idea that each individual, male or female, contains within itself the characters of the opposite sex. He thinks that this holds for the gametes as well as for the somatic cells. Darwin held a similar view and thought that this was true not only for the primary sex-cells (sperm and eggs) but for the secondary sexual characters as well. To-day, however, it is clear that such a statement, at least in regard to the estabhshed cases of sex determination by means of sex factors, calls for a more definite THE ORIGIN OF GYNANDROMORPHS. 19 pronouncement as to the sense in which the phrase is employed; otherwise it is Httle more than a play on words. For instance, when one X chromosome is present the individual is a male, which means that one X plus all the rest of the cell makes a male, and when two X's are present, these two plus all the rest of the cell make a female. In what sense can such a statement be twisted to mean that each such combination contains in a latent condition the opposite condition? Compare the facts with a similar chemical situation and the absurdity of the inclusion hypothesis is evident. Maltose has the formula C12H22O11 and glucose the formula C6H12O6. One is twice the other minus one H2O. To state that maltose contains glucose latent or that glucose contains maltose latent is obviously absurd, yet this does not differ much from the view that each sex contains the opposite one in latent form. De Meijere thinks that gynandromorphs can be explained in "that the activation of the opposite sex (opposite to the one already under way) has started in, relatively later, after all the parts have taken on their definite positions ; many of the parts have gone too far in the first direction, i. e., they are too old, but those that have not may be turned aside and produce the oppo- ^ ^ site results."^ This view is offered to account for mosaics of sex char- acter. The bilateral gynandro- morph, he supposes, owes its origin to the above changes having taken place very early, even at the first division. De Meijere thinks ap- parently of effects being produced by external factors of some unknown kind rather than internal ones connected with a sex mechanism. His idea is too vague to be of use and too remote from present-day knowledge about sex determination to call for extended criticism. . Arnold Lang, accepting the same general conception of sex and expressing what he beheved to be the real relations by means of the formulae that Goldschmidt had advocated, offered another possible interpretation of gynandromorphs that is superficially exactly like the theory of chromosomal ehmination which the results in Drosophila show to hold for this insect. In fact, Lang's view, if divested of the unnecessary encumbrance of De Meijere's conception and of Gold- schmidt's formulae, is then identical with the theory of chromosomal elimination. For example, Lang represents the fertilized egg (one that will give rise to a female) by the scheme shown in text-figure 4. The primary sex characters for the male are M carried by a pair of TEXT-FIOURE8 4 AND 5. * See Goldschmidt'a view in respect to the rate of development of male and female orgaoa in the intersexes of the gipsy moth. 20 THE ORIGIN OF GYNANDROMORPHS. chromosomes that also carries the factors for the secondary sexual char- acter A. The primary sex character of the female is represented by F, carried by a second pair of chromosomes, and the secondary sexual character by G, both as before, carried in the same chromosome. In other words, the two pairs of sex chromosomes are (FG) (FG) and (MA) (MA) for the female, and, for the male, (FG) (fg) and (MA) (MA). Lang suggests that a loss by mutation takes place in females (as above) in the sense that one FG disappears and may now be repre- sented by (fg). The resulting division is shown in text-figure 5. The mutation causes the sex-balance in the cell on the right side to turn into a male, while that of the left remains a female. Lang appears to mean that the "mutation by loss " is the loss of a daughter chromosome. If we ignore the special interpretation of sex employed by Lang and borne out by his formulae, his view has several points in common with the hypothesis of chromosomal elimination. It should be noted, however, that there are also differences in the apphcation of Lang's and the present interpretation, when the question of the sex-linked factors is involved, because the two X chromosomes represented by Lang by FG, FG carry many other genes, besides those for sex, even some for secondary sexual characters. Which of these comes to expression in the hybrid gynandromorph depend on which FG is elim- inated and not on the resulting change in balance (epigenetic effects) between the FG's and the MA's. Furthermore, Lang's scheme in- volves the relation between two pairs of chromosomes (four in all) while in the actual case of Drosophila only one pair is needed to account for all the facts. Cockayne, in 1915, announced independently the same view of elimination that Morgan had published the year before. He had found several halved gynandromorphs, all of which showed the specific characters of both parents on both sides. Both parental nuclei must therefore have contributed to both sides. He points out that since the division into male and female parts sometimes coincides with other characters the latter must be carried by the sex chromosomes. Doncaster, in 1914, described binucleated eggs in Abraxas, each nucleus giving off its two polar bodies and each being independently fertilized. He suggests that gjTiandromorphs might arise from such eggs, but did not obtain any in the particular lines that showed such binucleated eggs. The two gynandromorphs in Abraxas that Don- caster described later (1917), and which are considered here on page 85, he did not attempt to explain by this condition. The gynandromorphs of Drosophila have been from the time of their first appearance in our cultures, about 8 years ago, a subject of general interest and discussion, especially by Muller, Sturtevant, Bridges, and Morgan. Their relation to the gynandromorphs in bees and to the theories of the origin of the latter has been constantly THE ORIGIN OF GYNANDROMORPHS. 21 under discussion. The critical evidence that shows that they were not due to separation of whole maternal and paternal nuclei was first obtained and published by Morgan (in 1914). Prior to that time Bridges (1913) had published an account of two hybrid gynandro- morphs, and had suggested that they were due to somatic non-dis- junction. By this term it was meant at the time that at an early embryonic division of a female the two daughter halves of one of the X chromosomes did not disjoin from each other to pass, as normally, into sister cells, but were included in the same cell, the other cell not receiving its half. The non-disjoining X was assumed to divide normally and the result was an X cell developing into male parts and an XXX cell developing into female parts. This hypothesis served to explain all the facts known at that time. Soon, however, it was established (Bridges, 1916) that XXX individuals are unable to sur- vive, and this brought into question the conclusion that the female parts of gynandromorphs were XXX. This difficulty was later avoided by the assumption of ''elimination" (earlier called "mitotic dislocation," Morgan, 1914). As already stated, this meant that one of the daughter X's was caught by the mid-plate and prevented from taking its place in either nucleus. There is another class of gynandromorphs (including here four cases) in which another procedure may account for the results. Primary equational non-disjunction occurred, as evidenced by the presence in each of the four gynandromorphs of two X chromosomes from the mother, one of these being a non-cross-over and the other a cross-over X, as is usual for XX eggs produced in this fashion. This XX egg was then fertilized by an X sperm, giving an XXX individual. This XXX zygote is prevented from dying and at the same time converted into a gynandromorph by the occurrence of somatic reduction at the first or a very early embryonic division. In each of the four cases the male parts of the gynandromorph were derived from one of the two maternal X's, which suggests that the essential feature of this somatic reduction is the active separation of the two X's that came from the mother and the passive inclusion of the X from the father with one or the other of them. There have been other cases which may support this view, cases in which XX eggs equationally produced have been fertilized by Y sperm, and then the two X's have likewise reduced, with the result that each cell gets one X, and the entire individual is converted into a male which is a mosaic of different parts clearly marked by the character corresponding to the two dif- ferent X's. The difficulty with this view is that it assumes that reduction can take place between two X's at a cell division without the X's themselves splitting, although all of the other chromosomes do so at this time — a situation for which no support is given by cytology. It is to be noted in this connection tliat all cases that appear 22 THE ORIGIN OF GYNANDROMORPHS. to belong to this category are also explained by the assumption that the egg started with two nuclei, and in the description of cases both of these views are given as alternatives. THE ORIGIN OF THE GERM-CELLS IN FLIES. In several species of flies {Miastor, Chironomus, CalUphora) it is known that the germ-cells of the ovary or testis arise from a single cell at an early stage in the cleavage. In Miastor, for instance, when the four first-formed nuclei divide, one of the eight daughter nuclei moves to one pole of the egg, where it becomes surrounded by the peculiar protoplasm of this pole and subsequently pinches off from the surface of the egg. From this single cell by later division arise all of the germ-cells. A similar process has been described for other species of flies. If this holds also for Drosophila it follows that all of the germ-cells must be either eggs or sperm, regardless of whether the somatic parts are male or female. On the other hand, if the germ- cells in Drosophila and in the bee are formed as in some of the other insects, i. e., in the beetle Calligrapha described by Hegner, where 16 cells simultaneously reach the polar field, it would be possible for some of the cells to have descended from one of the first two segmentation nuclei and some from the other. In such a case, if the first-division figure underwent elimination, both ovaries and testes might appear in the same individual. In butterflies and moths, where many gynan- dromorphs have been dissected, several cases in which both testes and ovaries occur are known. This is also the case in bees. A difference in the time of isolation of the germ-cells in these groups and in Dro- sophila may account for the difference in the results. COURTSHIP OF GYNANDROMORPHS. Sturtevant's paper on sex recognition and sexual selection in Dro- sophila gives a full account of the rather elaborate courtship of this fly, in which the behavior of the two sexes is quite different. The re- actions of an animal, male on one side female on the other, or of one that had a female head and a male abdomen, might be expected to furnish interesting conclusions as to the relative importance of the sense-organs versus the reproductive organs in the behavior during courtship. Sturtevant tested 6 gynandromorphs. One was male throughout, ex- cept the genitalia, which were female. It behaved as a male. Sections of the abdomen showed one abnormal egg present. Another had 2 sex- combs, right and left, and the right wing was shorter than the left. The abdomen was female. She produced at least 1 egg. Sections of the abdomen showed 2 large eggs and a degenerate ovary present. She courted and was courted, thus giving both reactions. A third was THE ORIGIN OF GYNANDROMORPHS. 23 male, except the genitalia, which were female. Sections showed an abnormal testis near posterior end. It courted and was courted. Sturtevant records observations on three other gynandromorphs tested for sexual behavior: "None showed any certain indications of male behavior, but all were vigorously courted by males. Of these three gynandromorphs the external characters were as follows: (A) All female, except one side of the head, which was male; (B) female on one side of the whole body, male on the other side; (C) female, except the genitalia, which were male." Duncan describes the behavior of a bilateral gynandromorph. Its mating instincts were found to be indifferent. It was courted by males but would not court females. The gonads were both testes with ripe sperm. In a second gynandromorph, the eyes were female, but the forelegs had sex-combs; one wing was long (female); the ab- domen was male type, but the genitalia were half male, half female. Two ovaries were present. The fly was courted "assiduously" by males but would not mate. A third gynandromorph was without sex-combs on the forelegs, the wings were the same length, but the abdomen was male on one side, female on the other, as were the external genitalia also. Mature sperm were present in both testes. This fly was anteriorly female and posteriorly half male and half female. A normal male courted this gynandromorph when in front, but did not copulate wdth it. The gynandromorph drawn in text-figure 34 was tested by one of us (Morgan, T. H., Amer. Nat., 1915, p. 246). One side of the head and thorax is male, the other side female. The abdomen is pig- mented above as in a male and there is a penis below. When put with mature unmated females it did not court them, although it was quite active. Attempts to breed from gynandromorphs have been often made. It was not to be expected that those in which the genitalia were mixed would successfully copulate. Those with female abdomen have more often given offspring. Since, as explained elsewhere, the gynandro- morphs with male abdomen would not be expected to be fertile (be- cause the XO combination has been shown to be sterile), the frequent failure to obtain offspring from such males is in accordance with ex- pectation. On the other hand, an occasional fertile male gynandro- morph occurs. In these cases the combination was known or suspected of being XXY, the presence of the Y chromosome making the male (XY) fertile. PHOTOTROPISM IN MOSAICS WITH ONE WHITE AND ONE RED EYE. On several occasions it has been observed that when a mosaic had one red and one white eye it circled to the red side. This beliavior is expected from observations by McEwen on the light reaction of flies 24 THE ORIGIN OF GYNANDROMORPHS. from white-eyed stock. He showed that these flies respond much less actively to hght than do red-eyed flies. In these red-white mosaics the red eye, giving a stronger positively phototropic reaction, turns the fly toward that side. Of course, if the fly turns toward a single source of illumination, such as a window or artificial light, the red eye will soon pass into its own shadow as the fly turns, and the con- dition on the two sides may become balanced, unless the general illumination from the wall of the room, for instance, is still stronger than the influence of the window's light on the white eye. In order to avoid this complication the fly should be kept on a vertical surface held at right angles to the light, when its circus movements are not interfered with by the opacity of its own body. Since the male side of the body, including the legs, is generally smaller than the female side, and since the male side is the one that has the white eye, there is a chance that the movements toward the red side are against the stronger action of that side. This complica- tion was, however, not realized in all the cases in which circling occurred, but since in several of them the legs on the right and left sides were the same it is practically certain that the results are largely, if not entirely, due to the difference in stimulus from the two eyes. SEX-LIMITED MOSAICS. By a sex-limited character (in contradistinction to a sex-linked) we mean a character that is peculiar to one or the other sex, but is not necessarily transmitted by means of a gene in the sex chromosome. Such a character is shown by a stock called white tip, in which the pigment bands are absent from the last segments of the abdomen in the female but not in the male. In this stock a gynandromorph arose (text-fig. 6), male on the left side and female on the right. On the male side the black tip to the abdomen is present, although here, as in the stock itself, it is not as black as in the wild type. On the female side the abdomen has a white end. In this case elimination of a sex chromosome produced the gynan- dromorphous condition, and since in this stock the female parts are different from the male, owing to a factor presumably not in the sex chromosome, the right side of the gynandromorph also shows this peculiarity, owing to its femaleness. A similar case appeared (No. 2864, Jan. 1915) in a cross between a faint-band female and a star faint-band male. Faint-band is a sex- linked character which appears only in the female. All of the flies of the above cross were pure faint-bands; but while the females were characterized by abdominal bands in which both chitinization and pigmentation were weak and by short, slender, and irregular bristles throughout, the males could not be distinguished from wild males in appearance. The gynandromorph was completely bilateral, the THE ORIGIN OF GYNANDROMORPHS. 25 right side being male, with sex-comb, smaller eye, wing, etc., and the right side of the abdomen with male coloration. The genitalia were half-and-half also. The interesting feature was that throughout the female left side the bristles were weak and irregular and the bands "faint, " while the male right side was entirely wild-type in appearance. Another striking case appeared (on March 23, 1916) among the offspring of a pair, the female of which was heterozygous for the sex- limited character (" side-abnormal") and the father was pure for it. The character "side-abnormal" is sex-linked in inheritance and sex- limited in appearance, being seen only in females. In this mutant the bands of the abdomen of the female are "abnormal" at the sides, i. e., while the mid-dorsal part of the band is normal the ends of the band where they come around the side are cut away irregularly to ragged points and the color is etched with white splotches in the dark. The ventral plates are much smaller and are irreg- ularly rounded. In the male all parts are as in the wild flies. This gynandromorph (3806) showed a nor- mal male right half of the abdomen and a female left half, with all the characteristics of the side-abnormal character. The ven- tral plates were full and normal in the male parts and small and irregular in the female parts. Other evidences of maleness were present — a sex-comb on the right foreleg and a smaller right wing. Elsewhere in the text we have described several other cases involv- ing characters both sex-linked and sex-hmited. Thus in gynandro- morph 7530, page 46, the male eye on the right showed marked devel- opment of the character facet, as in the normal facet male, while the female left eye, also facet, could hardly be told from wild-type, as is usual in facet females. All gj^nandromorphs involving eosin eye-color show the Ught type of eosin in the male eyes and the dark t>T)e in the female eyes. Text-figure 6. 26 THE ORIGIN OF GYNANDROMORPHS. SOMATIC MOSAICS. Somatic mosaics can be accounted for by autosomal elimination in the same way that gynandromorphs are accounted for by X-chromo- somal elimination. Somatic mosaics might also be expected to arise from binucleated eggs and to be as often found as are gynandromorphs with the same origin. As a matter of fact, we have found only one certain case, which is less than expected on the latter view. The case is as follows : -^ The grandmother was spineless (third-chromosome recessive) and the grandfather was spread (another third-chromosome recessive). The daughters and sons were wild-type. A pair of these gave a 2 : 1 : 1 : 0 ratio, as expected, because of no crossing over in the male. One of the granddaughters (No. 561, Oct. 3, 1914, text-fig. 7) was a mosaic of spineless and not-spineless. The left side of the thorax and abdomen and the left wing and the middle and last left leg were spineless. The rest of the female (including all of the head and left foreleg) had long bristles and hairs of the wild type. Simple eUmination of the third chromosome from the spread parent would explain this case were it not that the existence of an individual lacking an autosome is doubtful, because none have as yet appeared through autosomal non-disjunction. On the alternative view of a binucleated egg, one nucleus contained the spineless third chromosome, the other a spread-bearing chromosome ; both nuclei were fertilized by X sperm bearing the spineless X chromosome, and gave the female spineless on the left side and wild-type on the right side. The fact that the overwhelming number of hy- brid mosaics are gynandromorphs, involving there- fore the sex chromosome, can not be explained as due to failure to discover autosomal mosaics if they occurred. In most of our cases these would be just as striking as in the cases where the sex chromo- somes are involved. Evidently some peculiarity in the separation of the halves of the sex chromosomes makes the elimination of one of the daughter halves more probable than in the case of other chro- mosomes. Such a supposition is, of course, in harmony with the pecu- liar behavior of the sex chromosome at the reduction division of the male, at least when it lags on the spindle. On the other hand, when it does divide, as in the female, no such peculiarity is recorded, and it is this reduction, rather than the former one, that we need for com- . parison. Text-figure 7. THE ORIGIN OF GYNANDROMORPHS. 27 SOMATIC MUTATION. That mutation may take place in somatic cells comparable to the mutation process in the germ- tract can not be doubted. The bud- sports long familiar to botanists probably furnish in some instances examples of this sort; but the best authenticated cases are the modern ones that have been analyzed by recognized genetic methods, P'ew examples are known to zoologists; the monsters, freaks, and duplica- tions that are frequently found are generally due to environmental effects on the embryo. If somatic mutation occurs in only one chromosome of a pair, as seems to be the case with germinal mutations, the immediate result will not be seen except when the mutation is dominant. In the case of mutation in the germ-tract, a recessive gene in one chromosome of a pair may Hkewise not have opportunity at first to express itself, but if it is carried to one of the offspring it will there become multiplied and get into daughters and sons (or in hermaphroditic species into pollen and ovules). Chance union of the gametes that contain the mutated chromosomes will later bring even the recessive genes to expression. It is more probable, therefore, that recessive mutations will appear in the sexually reproducing species more readily than in those with vegetative reproduction, except where the latter are already heterozygous. The same comparison may be made between parthenogenetic species and sexual ones. In the former, a recessive mutation appearing in one chromosome of a pair will have no oppor- tunity to show effects, and the line may be lost by chance alone. Preservation will be favored only if the heterozygous state has an ad- vantage over the original form. Sexual reproduction, therefore, has the advantage that every recessive mutation will have a far better chance of showing itself as a character modification and, if beneficial, of being preserved by natural selection. In fact, if it could be shown that a preponderant number of recessive mutations have furnished the material for evolution, it might possibly appear that we had some hint as to how the process has come to be such an almost universal method of propagation. On the other hand, dominant mutations might flourish, as well by the one as by the other method. The best authenticated case of somatic mutation in plants is that described by Emerson, who has brought forward convincing evidence that in corn a gene for certain types of variegation (striped seeds) mutates not infrequently to a gene for uniform-colored grain. The gene for medium variegated "mutates much more frequently than that for very light variegation. " By crossing pLants from the nuitated grains to pure recessive types Emerson has shown tliat when the mutation occurs it involves only one member (at a time) of the pair of allelomorphs in question. In these cases the mutation takes place in cell lines (subepidermis) that may ultimately contribute both to 28 THE ORIGIN OF GYNANDROMORPHS. the germ-tract and to the soma. Through the former, inheritance becomes possible, through the latter the effects of the mutation be- come visible only on the plant in which the mutation took place. There are other mutative changes in corn that Emerson describes in which the effect is only in the epidermal cells; hence, while it becomes visible in the plant in which it has taken place, it is not inherited, since the germ-tract does not come from this part of the plant. In the course of our work on Drosophila a few flies have appeared with characters which seem to have arisen by somatic mutation. If, as there is reason to suppose, the mutation changes that gave rise to them appeared in only one chromosome, the change must either have been dominant or, if recessive, in the single X chromosome of the male. Since visible mutations in the sex chromosome have been shown to be at least four times as frequent as dominants in all of the chromosomes together, the chance that these sporting characters are dominants is smaller than that they are recessive and in the sex chromosome. In support of the latter is the fact that nine out of ten of the sporting characters look like known sex-linked genetic char- acters, and more important still is the fact that all the cases so far found are males. (1) One of these somatic sports is shown in plate 1, figure 4. The right side of the body is pale, almost white. The history of this fly is as follows '} One of the X chromosomes of the mother contained the genes for lethal 7 and for forked, the other X the genes for yellow and for white. The X chromosome of the father carried the genes for yellow and for white. The fly was a yellow white forked male throughout, but the right side of the thorax, the right wing, and the right side of abdomen were pale, almost white, as shown in the drawing. Testes were present, with sperm. The pale light side is clearly due to somatic mutation, since no such pale body-color was present in the cross or was known elsewhere. Whether the mutation oc- curred in the X (if recessive) or in an autosome (if dominant) is undeter- minable, since the fly was not bred. (2) In another case (II 108, Oct. 21, 1913), the left side of the body, at least for a middle section, is brown in color, looking like the double recessive yellow black (text-fig. 8). The fly had the following history: Some F2 blacks from the cross of black by jaunty (both second-chromo- some) were inbred in an attempt to secure the double recessive black jaunty. One of the F3 black males had the left side of its thorax and abdomen, left wing, and left legs colored like the double recessive yellow black. It was at once assumed that mutation to yellow had occurred in the early embryo in the cells which gave rise to the left side. A test was made to see whether the germ-cells carried the mutant gene. The mosaic male was outcrossed to a black female and gave only black offspring (M69, black 9 27, black cf 23). Three pairs and a mass-culture of these Fi flies were inbred and gave a total ^No. 2493; November 20, 1915. THE ORIGIN OF GYNANDROMORPHS. 29 of 152 black 9 and 147 black cT, with no yellow-black offspring. Evidently, then, the testes came from a cell which had not mutated. While the "brown" color of the mosaic was like that produced by yellow acting with black, it is possible that the mutant gene was not the yellow already known, but a new yellow. (3) Among the grandchildren of the kst somatic sport a fly was found with a wing of an unusual type (text-fig. 9). This wing was about half the usual length and had almost exactly the form of min- iature, but there was none of the dark color normally present in miniature wings. This wing seems to have been a new mutant type, the mutation having occurred in the early embryonic cells of the fly. There have been quite a number of such occurrences, some, as in the present case, giv- ing striking differ- ences. (4) A fly ap- peared in vestigial stock (August 13, 1912) with one normal wing (text- fig. 10). It was described as a case of somatic atav- ism. An alterna- tive view is also possible, viz, that a somatic muta- tion occurred else- where, i. e., in an- other chromosome or in another region of the second chromosome, of such a sort that it neutralized the effect of both genes for vestigial. In the cells containing this mutant gene the conditions for normal wings are again restored. (5) a nd (6) Two further cases of mutation in the male were found by Sturtevant (not published); both were males throughout; one had forked bristles on one side of the body, although there were no forked flies in the immediate ancestry. The other had a dark body-color on part of the thorax, there being no sex-hnked dark body-color in the ped igree. Neither fly was tested. (7) I n a stock pure for red eyes, miniature wings, and j^ellow body- color a fly appeared with all the characters of its race except that one eye w as white with a fleck of red at its posterior edge (text-fig. 11). Text-figure 8. TEXT-nOCRE 9. 30 THE ORIGIN OF GYNANDROMORPHS. Since there was no white in the stock, the white eye must have come by mutation and possibly by mutation to a sex-Hnked white-eyed gene. (8) In a mating in which both parents were pure bar-eyed flies a male appeared (1917) (text-fig. 12) in which both eyes were round and in addition one eye was three-quarters white, and the other had a fleck of white in it. A germinal mutation in the mother of bar to round eye must have taken place, as shown by the fact that when the fly was bred it produced only normal-eyed offspring. Since this male was normal, it must have come from the union of a Y-bearing sperm and an X egg. Since the bar gene is carried by the X chromo- some, it follows here that mutation must have occurred in one sex chromosome of the mother. It is significant in this connection to call attention to the fact that bar-eye not infrequently mutates (reverts) to normal, as May has clearly proven. The other change to white was due to a somatic mutation. (9) In stock pure for black and for miniature and impure for white and for red eyes a male appeared that had one white eye (text-fig. 13). It might appear here that simple elimination in a heterozygous female would account for the white eye, but if the fly arose in this way the rest of it should be female. Double elim- ination will, however, give a result of this kind, i. e., a red X is lost from one half and a white X from Text-figure lo. the other side, leaving both parts male, one red, the other white. If, on the other hand, the fly started as a red-eyed male and dislocation occurred, so that most of the fly had an X, the other part a Y chromosome, the expectation, based on the evidence from nondisjunction, would be that the male part would die. However, it might be claimed that the evidence appHes to the fly as a whole and not to the survival of a small part of the body, which might very well be capable of living. But we should expect the absence of X to carry other consequences in its train besides loss of eye-color, so that this explanation seems improbable. A third explan- ation is that of somatic mutation. It is not possible to decide between the assumption of double elimination and that of somatic mutation. (10) A somewhat similar case is shown in the male figured in plate 1, figure 5. Its ancestry is not now a matter of record, but probably it arose in red-eyed bifid stock that we had at the time. If so, double elimination is excluded and the fly must have arisen by mutation in the sex chromosome. THE ORIGIN OF GYNANDROMORPHS. 31 It is a matter of great interest to find tliat all the ten cases of somatic mutation that we have recorded in Drosophila have been males. The significance of this was not appreciated until the material had been sorted out for other purposes. It probably means that a recessive somatic mutation takes place in the sex chromosome and shows at once in a male in those parts of the body whose cells contain the mutant gene because the male has only one sex chromosome. Should a reces- sive mutation occur in the X chromosome of a female its effect would not appear in the soma because the normal allelomorph would conceal it. It is interesting to apply this point of view to certain results in Lepi- doptera in which mosaics or gynandromorphs have been recorded that carry in parts of the body characteristics that are known to occur, although rarely, in varieties of sports of the species. Text-figuke 11. Text-figure 12. Text-figure 13. Among these a number have been described with one half of the body of one species and the other half of a varietal type of the same species. In some cases the variety is so rare that there might seem to be no question of a hybrid cross involved, since this in itself would be rare, and that both this and a later mosaic condition result is beyond reasonable probability. An alternative view would be that of somatic mutation. If such were the explanation we should expect the indi- vidual to be female and the mutation to have occurred in the single Z chromosome. In the cases brought together by Cockayne, in which the same individual is partly one species, partly a variety (1915, pp. 87-90), there are about 10 such cases recorded as females, 2 as males; in 12 cases no sex is stated by Cockayne. If further examination of the original sources shows as high a percentage of females as in the recorded cases, the evidence is in favor of the interpretation suggested above. The males call for another interpretation, and each such case will need special examination. 32 THE ORIGIN OF GYNANDROMORPHS. These cases are not to be confused with mutation in the germ- tract, where, in a sense, the reverse situation is realized, for while in Drosophila the mutation of a sex-linked character in one female chromo- some appears immediately in one (or more) of her sons, the mutation itself occurred first in the female. Conversely, in moths, if a germ- tract mutation took place in the male it would show immediately in one or more daughters. The well-known case of Abraxas grossulariata may be taken to show why mutation taking place in a male is expected to show first in the female and not in the male offspring. The genetic evidence for Abraxas indicates that the female has one sex chromo- some, the male two. The aberrant form lacticolor is found occasion- ally in nature and is always female. A mutation to lacticolor in a Z chromosome of the male would give rise to a daughter if this sperm fertilized a not-Z egg that would at once show the sex-linked character lacticolor. MOSAICS IN PLANTS. The cause of variegation in plants is too involved and obscure^ to attempt to discuss in this connection. On the other hand, the occurrence of bud-sports is generally recognized as due to somatic mutation which may include the germ-tract also. The frequent occur- rence of bud variation in the cultivated forms of the foliage plant Coleus has recently been studied by Stout, who has obtained from a single plant (and its clones) a number of types differing both in color and form of the leaves. The cultivated varieties have arisen through hybridization. Three interpretations suggest themselves as possible. Elimination of the chromosomes of the hybrid might account for the results, but no information as to the chromosomes in the different types is available. If any of the colors are due to cytoplasmic plastids, their irregular distribution might also be responsible for the result. Thirdly, the change might be due to a, mutation. If the types studied are complex hybrids with one or more heterogeneous pairs of chromo- somes, a change in one gene of one chromosome might bring about directly a \'isible change in the color. Until more critical Mendelian work is done it is not possible to reach any plausible or even probable conclusion. It might be possible to analyze the results more closely if we knew what kinds of offspring arise from the original plant and its varieties. Owing to the complex nature of the plants this pro- cedure offers difficulties. A few facts are given by Stout. He states that "plants grown from seed give wide variations .... Many of the types that had appeared as bud variations appeared also in the seed progenies." Winkler produced mosaics by grafting tomato and nightshade, which are now supposed to be due to a combination of the tissues of the ' Except in the case of Pelargonium and of Mirahilis, where Baur and Correns have shown that the mosaics are caused, in some instances at least, by plastid assortments. THE ORIGIN OF GYNANDROMORPHS. 33 two plants — the epidermis of one species and a core of the other s{x?cie8. The mosaic shown in Cytisus adami, a hybrid resulting from fi;raftinK Cytisus purpureus and Laburnum vulgare, seems also to be due to a similar sort of combination. In animals mosaics have been produced in hydra by King by grafting pieces of a deep-green race on a light one, and by Whitney by destroying the green pigment of one indi- vidual and grafting pieces of it onto a normal green hydra. In tad- poles combinations of different species caused by grafting have been made by Born, Harrison, Morgan, and others. A result strictly comparable to the periclinal chimaeras of plants has been reached by grafting a piece of the tail of one species on to the amputated stump of another species. As the new tail grows the skin of the stock is carried out over the core derived from the graft, and as a result an organ is formed with an outer layer of one and a core of another species. The mosaic seeds of corn that are striped with red and white have been shown by Emerson to arise through a mutation in the gene for striping. The ''half-and-half" mosaic grains that have been recorded by Correns (1899), Weber (1900), East and Hayes (1911), Emerson (1915), and Collins (1919) have been variously accounted for — re- calling the different interpretations that have been advocated for gynandromorphs in animals. Emerson (1915) reviews these theories and advances the explanation of somatic mutation. It seems not improbable that elimination will account for those mosaics in which the triploid endosperm nucleus is involved. CLASSIFICATION AND DESCRIPTION OF GYNANDROMORPHS OF DROSOPHILA. The main group includes the gynandromorphs that are adequately explained by chromosomal elimination. It is subdivided according to the type of gynandromorph into : (1) those approximately bihiteral, (2) those mainly female, (3) those mainly male, (4) those in which the type is largely "fore and aft," and (5) those in which the mother was known to have been an XXYfemale, but in which simple elimination is sufficient to account for the results. Another group (6) includes those in which the distribution of parts is irregular. These types are only approximations and by no means mutually exclusive; it is often somewhat difficult to decide to which type a specimen belongs. The highly interesting group of special cases (7) is undi\ided, though it calls for three or four different genetic explanations, based, however, on special modes of distribution of the sex chromosomes. In the Appendix are included those cases in which our records are incomplete as to parentage or in which the specimen has been lost, so that the description is sketchy. This grou]) contains many of the very early gynandromorphs. To this subdivision is added a brief review of previously pubhshed gynandromorphs in Drosophila. 34 THE ORIGIN OF GYNANDROMORPHS. Within each subdivision the arrangement of the cases is according to the order of discovery, that is, by date, except that the colored figures are taken out of order and described first in each group. Each case is known by a number, which is usually that of the culture bottle in which the gynandromorph was found, but in some cases letters or small numbers are used, which, however, correspond to the bottle in which the specimen is preserved or the order in which the descriptions were first arranged. The date, the finder, and the type of illustrations are also indicated on the number line. The information on each case is then given in the order. Parentage, Description, and Explanation. In many of the cases the explanation is followed by a diagram showing at the left the two X chromosomes of the zygote, which at the same time represent the female parts of the gynandromorph, and at the right the single X that is left after elimina- tion, which gives the constitution of the male parts. In case somatic reduction was involved the leftmost set of chromosomes represents the initial condition of the zygote, and the other two sets to the right the resulting two conditions, whether male or female. A knowledge of the order and the relative spacing of the genes along the chromosome is indispensable, and we have therefore made a list of the sex-linked mutants mentioned, with their symbols and the approximate locus of each : Mutant. Symbol. Locus. Mutant. Symbol. Locus. Sable duplication . . . Lethal 6 S le y h w w« w* N fa b« h 0.0 -0.004 0.0 0.3 \ 1-1 1 2.6 6.3 / 7.0 12.5 Club Cut c« t V m h a g u r f B f« 16.7 20.0 27.5 33.0 36.1 38.0 43.0 44.4 45 ± 49.0 55.1 56.5 57.0 59.5 65=fc Yellow Tan Lethal 7 Vermilion White Miniature Eosin Lethal 9 Blood Sable Cherry Garnet Notch Rugose Facet Lethal 4 Bifid Rudimentary Forked Bar Ruby Claret Crimson Lethal 2 Fused Cleft The figures in the plates are camera-lucida drawings of etherized living flies, but in the following descriptions of the gynandromorphs diagrams only are given (except in rare instances). These diagrams were made from the flies themselves, which are preserved in alcohol. All drawings and diagrams were made by Miss Edith M. Wallace, to whose skill and accuracy they bear witness. PLATE 2 \ TtHwC J \ ■ 4;i X!# ^- s \y<- v.. \1. w M.I.ACK I'mx GYNANDROMORPHS OF DROSOPHILA THE ORIGIN OF GYNANDROMORPHS. 35 Approximately Bilateral Gynandromorphs. No. Giad2. Feb, 1914. E. M. Wallace. Plate 2, Figure 1 (colored drawing). Parentage. — The mother wavS a white-eosin compound female from the cross of a yellow white female to an eosin male. The father was a yellow white male. Description. — The entire head, the right half of the thorax and of the ab- domen, the right wing, and all of the right legs were gray and female. Both eyes were white-eosin compound and therefore female, which was in agree- ment with the gray color and black bristles of the whole head. The genitalia were apparently entirely female. The left side of the thorax and of the abdomen, the left wing, and all of the left legs were yellow in body-color, smaller, and male. There was a sex-comb on the left side only. The gynan- dromorph failed to produce offspring when tested. Explanation. — An egg with the eosin-bearing X was fertilized by the X sperm bearing the genes for yellow and white. The zygote was therefore female, and the female parts of the gynandromorph have this constitution. At the first segmentation, division elimination of a maternally-derived eosin- bearing X occurred, giving rise to a cell with only a yellow white X. The parts descended from this cell were male and showed the yellow body-color corresponding to the yellow white chromosome. Since neither of the eyes was male, the white eye-color had no chance to show on the left side. w I y w y w No. GaCisa. Feb. 1914. E.M.Wallace. Plate 2, Figure 2 (colored drawing). Parentage. — A mass culture of the white-eosin compound females (eosin in one X and yellow white in the other, from gynandromorph G2C19 above) out- crossed to yellow white males produced a further gynandromorph (G2C190). Description. — The gynandromorph, while yellow and white throughout, was a strict bilateral gynandromorph, including genitalia and antennae. The right side was male throughout, as evidenced by sex-comb, smaller size of bristles and of all parts such as eye, thorax, wing, legs, and abdomen, and by the male coloration of right side of the abdomen. The gynandromorph was tested but gave no offspring. Sections showed slightly developed ovaries on both sides. Explanation. — An egg containing the X with the genes for yellow and white was fertilized by an X sperm likewise carrying the genes for yellow and white. Elimination at the first segmentation division of a maternal or of a paternal X, gave a cell with a single X, from which is descended the male right side. y w yw yw No. 77. March 10, 1914. C. B. Bridges. Text-figure 14 (diagram). Parentage. — The mother was homozygous for eosin and heterozj'gous for a non-sex-linked gene "cream," which is a specific dilutor for eosin (Bridges, 1916). The father had the same constitution. Description. — The gynandromorph was completely bilateral "from head to tail." The right side was male with a sex-comb and smaller jKirts. The abdomen had the female coloration above, but below was divided iialf and half, as were the genitalia. The eyes were both "cream," that is, of diluted 36 THE ORIGIN OF GYNANDROMORPHS. eosin color. The right male eye was much lighter than the female left eye, as is the rule with eosin even when diluted. Explanation. — Both egg and sperm carried the genes for eosin and cream. Elimination of the paternal or of the maternal X occurred. Presumably the autosome carrying the cream gene behaved normally as in all known cases, but this case is not diagnostic, since the fly was homozygous for cream. w^ w^ w^ Text-figure 14. Text-figure 15. Text-figure 16. No. 1-5. A.M.Brown. April 9, 1914. Plate 2, Figure 4 (colored drawing) . Parentage. — The grandmother was homozygous for vermilion and hetero- zygous for a lethal. The grandfather was eosin-miniature. A gynandro- morph was produced by one of their wild-type daughters which had been out-crossed to an eosin-miniature male. Description. — The right side was male throughout with an eosin (male color) eye and miniatm-e wing. A sex-comb was present on the right foreleg. The left side was entirely female, with red eyes and a long wing. Explanation. — A non-cross-over egg containing the wild-type X was fertil- ized by an X sperm with genes for eosin and for miniature., Ehmination of one of the maternal X's left the male parts eosin-miniature. w m w^ m No. 195. April 27, 1914. C. B. Bridges. Text-figm-e 15 (drawing). Parentage. — One X chromosome of the mother carried the gene for white eye-color and the other X the genes for eosin and for lethal 4. The X chromosome of the father carried the gene for sable. THE ORIGIN OF GYNANDROMORPHS. 37 Description. — The right side of the gynandromorph was male, with a white eye (with a fleck of red in it) and a sex-comb. The right wing was smaller. The genitalia were mainly male, but also with some female parts. Testes were found in sections of the abdomen, with plenty of sperm. Explanation. — An egg containing the white X wa-s fertilized by a sable- bearing X sperm. A paternal sperm suffered elimination, leaving the white- bearing X to produce the male side. The female side is wild-type, since one X has the normal allelomorph for white (viz, red eye), and the other X the normal allelomorph for sable (viz, wild-type body-color) . w w No. 1373. February 22, 1915. C. B. Bridges. Text-figure 16 (diagram). Parentage. — One of the X chromosomes of the mother carried the genes for eosin and for vermilion, and the other X the genes for sable body-color and forked bristle. The X chromosome of the father carried the dominant gene for bar. Description. — The left side of the gynandromorph was male throughout, being of smaller size in head, thorax, abdomen, wing, bristles, and legs, and having a sex-comb. The right eye was e 'sin-vermilion in color and not- bar. The coloration of the abdomen was male on the left side at the tip, and the genitalia were very largely male. The right side was female, with a red-bar eye. The abdomen was sectioned and found to contain a pair of poorly developed ovaries. Explanation. — An egg containing the X chromosome with genes for eosin and for vermilion was fertilized by the bar-bearing X sperm. Elimination of a paternal X chromosome left the eosin-vermilion-bearing X to produce the male side, while the female side contained the dominant allelomorphs for these two genes, as well as the dominant gene for bar eye in the female XX complex. B No. D. From Lethal 2 Stock. May 1, 1915. E. M. Wallace. Text-figure 17 (diagram). Parentage. — The wild-type mother carried lethal 2 in one X and the genea for bifid and tan in the other. The stock was maintained by repeating in each generation the cross of wild-type lethal-bearing females to their bifid- tan brothers. Description. — The gynandromorph was completely bilateral, the left side being male and the right female. The left side showed tan body-color through- out and had a bifid wing. The left side showed all the size, coloration, and other secondary sexual characters of the male. The genitalia were male. Sections showed that two rudimentaiy ovaries were present. Explanation. — A non-cross-over egg containing the genes for lethal 2 was fertilized by an X sperm with the genes for bifid and tan. Elimination of I 38 THE ORIGIN OF GYNANDROMORPHS. one of the maternal lethal-bearing X's occurred with the production of bifid tan male parts. bi hi t No. 1818. July 4, 1915. C. B. Bridges. Text-figure 18 (diagram). Parentage. — One X chromosome of the mother carried the genes for sable and for forked; the other was wild-type. The X chromosome of the father carried the gene for forked. Description. — The gynandromorph was completely bilateral, the left side being male and the right female. The fly was not forked on either side. The genitalia were female. Sections showed ovaries on both sides. Text-figure 17. Text-figure 18. Text-figure 19. Explanation. — An egg containing the normal X chromosome was fertilized by the forked sperm. A paternal X suffered elimination, leaving a normal X to produce the male side. The female side was also normal, because the maternal X present carried the normal allelomorph of forked. / No. T. July, 1915. E. M. Wallace. Text-figure 19 (diagram). Parentage. — The parentage is unrecorded, but from the characters shown by the gynandromorph it is probable that the fly came from notch stock. The mother carried the dominant gene for notch wing in one X and the gene for eosin in the other. The father was eosin. Description. — The right side was male with a sex-comb, a short wild-tj^pe wing, smaller bristles, smaller half- thorax and half -abdomen. The tip of THE ORIGIN OF GYNANDROMORPHS. 39 the abdomen had male coloration on both sides and the genitalia were largely male. The right eye was eosin of the male type. The left side was mostly female with a red eye and a large notched wing. The gonads a.s seen through the body-wall seemed to be both ovaries. Explanation. — A notch-bearing egg was fertilized by an eosin sperm. Elimination of the maternal notch X occurred. N w' w Text-figure 20. No. F. January, 1916. T. H. Morgan. Text-figure 20 (diagram). Parentage. — The parentage of gynandromorph F is unrecorded, though it is probable that it was found in a wild stock. Description. — The fly was a completely bilateral gynandromorph having on the right side a sex-comb, shorter wing, shorter bristles, and smaller parts in head, thorax, and abdomen. The coloration of the abdomen was male at the tip on the right side, but female in the remainder. The genitalia were entirely female. The abdomen contained a fully developed pair of ovaries and she produced many offspring which were all wild-type. Explanation. — Elimination of one X occurred in a normal female zygote; whether this X was maternal or paternal is indeterminable. 40 THE ORIGIN OF GYNANDROMORPHS. No. 380. March 28, 1916. A. Weinstein. No diagram. Parentage. — The mother carried the genes for ruby and forked in one X and the genes for eosin and sable in the other X. The father was eosin-bar. Description. — The gynandro- morph was about half and half, the left side being mainly male and the right female. The left side of the head and thorax and the left wing were smaller and the left foreleg bore a partly double sex-comb. The left eye was eosin bar of the male type. The genitalia were double pos- teriorly; there was a penis with claspers and anterior to the right of this an ovipositor and female-type anal prominences. The abdomen was female in coloration, except at the tip on the left side, which showed the male banding. The right eye was red and of the broad hetero- zygous bar female type. Explanation. — A ruby forked X egg was fertilized by an eosin bar X sperm. Elimination of the maternal ruby forked X oc- curred. r' f Text-figure 21. W^ B We B No. SS01122AAA7344512 Selection Experiment. January 18, 1917. T. H. Morgan, Plate 4, Figure 1 (diagram). Parentage. — The mother was notch, having therefore one X chromosome with the dominant gene for notch; the other X carried the recessives eosin and ruby. The father was likewise eosin ruby. Description. — The gynandromorph was male on the right side, except for spots of red (female) in the eosin ruby eye of that side. The coloration of the abdomen was male throughout. The genitalia were mainly male, but showed female parts. The left side was mainly female, having a red eye and a notch wing of slight type. No gonads were found in the sections examined, but it is probable that there were very rudimentary ovaries. Explanation. — An egg bearing the gene for notch was fertilized by an X sperm with the genes for eosin and for ruby. Elimination of a maternal X chromosome left the male parts to be determined by the paternal eosin ruby X. N w" n w n PLATE 3 jW*-^' #2* w-^ 4 la 3. Normal $ v.* - • ^'~- ^ i 'W 3a. Normal f^ Sa?L r \ *UP' i;. M. Waulacic I'inx GYNANDROMORPHS OF DROSOPHILA THE ORIGIN OF GYNANDROMORPHS. 41 No. 29. February 11, 1918. T. H. Morgan. Text-figure 21 (drawing). Parentage. — Both mother and father were eosin. Des(rription. — The gynandromorph was bilateral, ex(!ept that the entire head was female, having eosin eyes of the dark liomozygous eosin color. The left side was male, having a sex-comb, shorter kigs, shorter bristles and wing, and a smaller left side to the thorax and abdomen. The coloration of the abdomen was half and half, but there appeared to be a pair of ovaries and female genitalia. Explanation. — An egg containing an X chromosome with the g(!ne for eosin was fertilized by an X sperm can-ying eosin. Elimination of either X gave the nearly bilateral gynandromorph. w* w' Gynandromorphs Mainly Female. No. C2C19. January 1914. E. M. Wallace. Plate 2, Figure 3 (colored drawing). Parentage. — The mother was white-eosin compound, having the genes for yellow and white in one X and eosin in the other X. The father was eosin. Description. — All of the fly was gray and female, except the upper right half of the thorax and the right wing, which were yellow and male. Both eyes were eosin, of the dark type of the homozygous eosin female. Well- developed ovaries were present on both sides. Mated to a yellow white male this gynandromorph was fertile and produced white-eosin females 70; eosin males 42; yellow white-eosin females 53; yellow eosin males 58. Explanation. — An egg with a cross-over X containing the genes for yellow and eosin was fertilized by an X sperm with a gene for eosin. Elimination of one of the latter left the maternal X to produce the male parts on the upper right side of the thorax. to* No. 5137. September 4, 1916. C. B. Bridges. Plate 2, Figures 5 and 5a (colored drawings). Parentage. — The mother had one chromosome with the genes for vermilion, sable, garnet, and forked, and the other X with the genes for vermilion and for bar. The X-bearing sperm carried the genes for eosin and for miniature wings. Description. — The mosaic was entirely female, except for a patch of eosin in the left eye. The eosin part of the eye was round and light eosin (male type) while red bar both above and below (very slight amount below). The right eye was red bar. The whole abdomen was full of eggs. Explanation. — An egg with the X chromosome carrying the genes for vermilion and bar was fertihzed by a sperm carrying the genes for eosin and miniature. Elimination of a maternal chromosome took place, leaving the 42 THE ORIGIN OF GYNANDROMORPHS. one X with eosin and miniature genes to produce the male parts, which in this case affected visibly only a part of the left eye. w^ in w" in No. M, 114. January 23, 1914. C. B. Bridges. Text-figure 22 (diagram). Parentage. — One of the X chromosomes of the mother contained the gene for eosin, the other the gene for bar. The father was white bar. Both parents were heterozygous for the autosomal recessive gene "whiting," which is a specific modifier of eosin. Description. — The gynandromorph was somewhat more than half female. The left side of the gynan- dromorph, except for the head, was male, with sex- comb, smaller bristles half-thorax and wing. In col- oration the abdomen was male on the left and female on the right. The genitalia were entirely female. The head had heterozygous bar (female) eyes, which were white-eosin compound (female) in color. A pair of ovaries was present. Explanation. — An egg containing the X chromo- some with the gene for eosin was fertilized by the X sperm with the genes for white and for bar. Either chromosome may have been the one to suffer elimination; which one it was could not be determined, since the head did not show male parts. No. 438. August 16, 1914. C. B. Bridges. figure 23 (diagram). Text- Text-fiqure 22. The X chromosome of Text-figure 23. W Parentage. — One X chro- mosome of the mother con- tained the genes for eosin and for vermilion, the other X the gene for white eyes, the male carried the gene for eosin. Description. — The left side of the gynandromorph was largely male with a white eye (containing a fleck of white-eosin), a sex-comb, and a shorter wing. The right side was female, with a white-eosin com- pound eye, no sex-comb, and a longer wing. The abdomen was banded like a female. When bred as a female the fly gave the classes expected for a white-eosin compound. No sections were made. Explanation. — An egg containing the X chromo- some with the gene for white was fertilized by an X sperm carrying the gene for eosin. The latter — the paternal chromosome — suffered elimination, leaving the white-bearing X to produce the male side. The color of the eye on the female side was white-eosin compound, which is the expected result for the two X's involved. ?/' W THE ORIGIN OF GYNANDROMORPHS. 43 No. 922. December 16, 1914. C. B. Bridges. Text- figure 24 (diagram). Parentage. — One of the X chromosomes of the mother contained the genes for eosin and for vermil- ion, the other X the gene for forked. The X chromo- some of the male carried the genes for white and for bar. Description. — The fly was female throughout (with- out sex-combs) and possessed white-eosin heterozy- gous-bar eyes, except that the tip of the abdomen on the left side was banded like a male. Below there was a normal penis and male armature. In sec- tions an ovary was found on one side, nothing on the other. Explanation. — An egg containing the X chromo- some with the genes for eosin and for vermilion was fertilized by the X-bearing sperm with the genes for white and for bar. Elimination of either X chro- mosome would account for the male parts at the tip of the abdomen. vf V t w^ Text-figure 24. or w B w B No. 925. December 18, 1914. C. B. Bridges. Text-figure 25 (diagram). Parentage. — The mother was club, carrying in one X the sex-linked gene club, and in the other X lethal 2 which is a deficiency for club. The X sperm of the father carried the genes for eosin and for miniature. Description. — The only male part was the right eye, which was eosin (male type) in color, except for a fleck of red (female). The fly was fertile as a female when mated to a wild male and produced: No. 1117; wild type females, 101; eosin miniature males, 55; miniature male, 1; eosin males, 9. Explanation. — An egg with an X bearing the gene for lethal 2 was fertilized by an X sperm with the genes for eosin and miniature. Elimination took place in one of the maternal chromosomes, leaving the paternal X with eosin and miniature to form the male parts, viz, the right side of the head (in part). The rest of the mosaic was female; hence both wings were wild-type. Cl w —r- m w^ m No. 1010. December 20, 1914. C. B. Bridges. Text-figure 26 (diagram). Parentage. — One X chromosome of the mother carried the genes for yellow and for white, and the other X the gene for lethal 6. The X chromosome of the father carried only wild-type genes. 44 THE ORIGIN OF GYNANDROMORPHS. Description. — The left side of the thorax of the gynandromorph was male, with a sex-comb and a shorter wing. Both eyes were red and female. The abdomen and genitalia were female. The body-color was wild-type through- out. Sections showed ovaries on both sides. Explanation. — An egg containing the lethal 6 X chromosome was fertilized by a wild-type X sperm. Either one of the X chromosomes being eliminated would account for the result. If the paternal X were eliminated the male parts would be lethal 6, and hence it is more probable that the maternal X was eliminated. /. I, or No. 1808. July 7, 1915. C. B. Bridges. Text-figure 27 (diagram). Parentage. — The mother was pure for the second-chromosome recessives purple, curved, and speck. The father was heterozygous for the dominant star (eyes). No sex-linked mutant characters were present. Text-figure 25. Text-figure 26. Text-figure 27. Text-figure 28. Description. — The gynandromorph was female throughout, except for the abdomen, which had male coloration on the left side and was twisted to the left. A perfect penis was present. The eyes were star. The male parts could not have shown the recessive second-chromosome characters, even had they been present. No testes or ovaries were found, but there was a genital tube with pointed cells like abnormal spermatozoa. THE ORIGIN OF GYNANDROMORPHS. 45 No. 5238. September 23, 1916. C. B. Bridges. Text-figure 28 (diiigram). Parentage. — One of the X chromosomes of the mother carried the genes for vermihon eye-color and for bar eye, the other X the gene for forked bristles. The X chromosome of the father carried the genes for eosiii, vermilion, and forked. Description. — The fly was mainly female, but is exceptionally interesting from the peculiar description of the male parts, which constitute a v(;ry narrow stripe running through the middle of the left eye and along the left side of the thorax, including the wing. The left eye was eosin vermilion in color in the male parts and red in the female parts, both above and below the eosin vermilion. These female parts were heterozygous for bar and the red portions above and below were therefore characteristically narrow, while the eosin-vermilion part was not-bar and projected forward, so that the male stripe could be traced forward to the normal margin of the round eye. The male part of the thorax could likewise be traced by means of the forked bristles, of which there were three anterior to the wing, one above, and none below. The wing itself was included in the male region and was smaller and had forked marginal bristles. There was no sex-comb on the left side. Explanation. — An egg containing an X chromosome with the gene for bar was fertilized by the eosin vermilion forked sperm. A maternal X suffered elimination, leaving the eosin vermilion forked X to produce the male parts. B W^ V f W V f No. 2. September, 1917. T. H. Morgan. Text-figure 29 (drawing). Parentage. — The fly appeared in "selected notch" stock in which, in each generation, red-eyed notch females were bred to eosin ruby males. Description. — The right eye was red, the left partly red, partly eosin ruby, with a very irregular boundary-line; other- wise the fly was female. Explanation. — An egg with a gene for notch wing was fer- tilized by an X sperm bearing eosin and ruby. Elimination of one of the maternal X's left a part of one side of the head with the eosin ruby X. The wings, although not showing notch, must have contained the gene. Since less than half text-fioure 29. of the notch flies in this selected stock showed the notch character, its absence here is not diflficult to explain. W Vb W' rb No. 477. October 31, 1917. D. E. Lancefield. Text-figure 30 (drawing). Parentage. — One of the X chromosomes of the mother had a bar gene, the other a gene for forked. The father was bar. Description. — The head was small, with round eyes and forked bristles. The thorax and wings seemed to be female. No sex-combs present. The abdomen was entirely female, with eggs inside, but she did not breed. 46 THE ORIGIN OF GYNANDROMORPHS. Explanation. — An egg containing an X with a gene for forked was fertilized by a bar X sperm. The paternal X with bar was eliminated, leaving the head male and forked. / / Text-figure 30. No. 71. October 23, 1917. E. M. Wallace. Text-figure 31 (drawing). Parentage. — Pure stock of bar. Description. — A female was observed that had a short left wing. Closer ex- amination showed that the bristles on that side of the thorax and head were shorter and that the left side of the head was sUghtly contracted and the eye smaller. It is probable that the left side of head and thorax (dorsally) were male. No. 7530. August 18, 1917. C. B. Bridges. Text-figure 32 (diagram). Parentage. — One of the X chromosomes of the mother carried the gene for facet eye and the other X the gene for notch wings (dominant). The X chromosome of the father carried the gene for facet. Description. — The left side of the gynandromorph was male, with a shorter wing, sex-comb, and smaller eye, whose markedly faceted eye was character- istic for that character as it appears in the male of the mutant type. The female side had a faceted eye of the female type, which is far less marked. The abdomen was banded as in the female, but below a penis was present. Testes were found on both sides, with an abundance of sperm. Explanation. — An X egg-carrying facet was fertiUzed by the X sperm- carrying facet. Elimination of either occurred. The gonads were formed from a male cell. Very frequently a male-appearing abdomen contains ovaries; only very rarely does a female-type abdomen contain testes. THE ORIGIN OF GYNANDROMORPHS. 47 No. Xi. January, 1914. E. M. Wallace. No diagram. Parentage. — This gynandromorph arose in a mass-culture whose parents were yellow white females and eosin males. Description.— The gynandromorph was largely female. The male parts were yellow and included the left dorsal side of the thorax with the shorter wing and the left side of the abdomen. These parts were all smaller, bore Text-figure 31. Text-figure 32. smaller bristles, and the left half of the abdomen had male-type coloration. The genitalia were female. The female parts throughout were wild-type in body-color, including especially the left legs and all the head. There were no sex-combs. The eyes were both white-eosin compound. Explanation. — A yellow white X egg was fertilized by an eosin X sperm. Elimination of the paternal X occurred. y w y w w^ 48 THE ORIGIN OF GYNANDROMORPHS. Gynandromorphs Mainly Male. No. GiAboCaz. March, 1914. E. M. Wallace. Plate 2, figures 6 and 6a (colored drawings). Parentage. — The mother was a yellow white female, a daughter of gynandro- morph GiAb2C. The father was an ebony (third-chromosome) male. This mating was part of the second of the tests specifically designed to show the absence of elimination of autosomes in the production of gynandromorphs. Description. — The gynandromorph was mainly male, with only the head and genitaha female. The color of the entire thorax, abdomen, legs, and wings was yellow, and correspondingly the bristles of these parts were brown. These yellow parts were male, as proved by the sex-combs on both forelegs, by the small (male) size of the bristles, of the thorax, and particularly of the abdomen, and by the male coloration and shape of the abdomen. However, the genitalia were an exception, for the anal prominence and the ovipositor were purely female in structure and bore black spines which showed that the body-color was wild-type. The head was entirely female, as proved by its large size, the wild-type color with black bristles, and by the red eyes. Thus the head and genitalia — the two ends of the fly — were female and all the region between was male. Explanation. — An egg carrying the genes for yellow and white was fertilized by sperm carrying only wild-t>T)e genes in the X. EUmination of a paternal X occurred and subsequent shifting isolated a female cell which gave rise to the genitalia. The absence of ebony proves that the third chromosome did not undergo elimination. y w y w No. X2. February 1914. E. M. Wallace. Text-figure 33 (drawing). Parentage. — Gynandromorph X2 appeared in a mass-culture, the mothers of which carried yellow and white in oneX and eosin in the other; the fathers were yellow- white. Description. — The gynandromorph was mainly male. The female parts were confined to the abdomen, which had female coloration on the left side and apparently male on the right. The abdomen was twisted to the right, which also suggests that the right side was male. However, the genitalia re- versed this relation, the right side being largely female, with an anal prominence of female type; the left side was male and there was a median penis. The abdomen was of large size and a pair of ovaries could be clearly seen within. The thorax and head were entirely male, as evidenced by their size and the type of bristles and the pres- ence of sex-combs on both forelegs. The eyes were both white and the body- Text-figure 33. color was yellow throughout. Explanation. — A yellow white X egg was fertilized by a yellow white X sperm. EUmination of either X occurred. An alternative explanation is that the egg was fertilized by a Y sperm giving a yellow white male. Somatic non-disjunction resulted in a cell with both daughter X's present, and this gave rise to the female parts. THE ORIGIN OF GYNANDROMORPHS. 49 No. 3. February 1915. T. H. Morgan. Text-figure 34 (drawing) Parentage. — The mother was rudimentary and the father bar. Description. — The gynandromorph was about three-fourths male. The right halves of the head and of the thorax were female, being larger in size, having larger bristles and a larger wing, which was wild-type, and no sex- comb. The right eye was heterozygous bar (female). The left eye was bar of the male type and the left halves of the head and of the thorax were male. The left wing was smaller, but not inidimentary. The abdomen seemed en- tirely male, with a normal penis. This gynandromorph was tested as to sexual behavior and was found to pay no attention to mature virgin females. An account of this gynandromorph and the drawing have been previously published. (Morgan, Am. Nat., V. 49, p. 240, April 1915.) Explanations. — An egg with a rudimentary X was fertilized by an X sperm carrying bar. Elimination of the maternal rudimentary X occurred. Some of the female 'cells were lost in cleavage, so that the individual is prepon- derantly male. Text-figure 34. Text-figure 35. No. 2317. November 2, 1915. C. B. Bridges. Text-figure 35 (drawing). Parentage. — One X chromosome of the mother carried the genes for rudimen- tary wing and fused veins, and the other X the gene for bar. The X chromo- some of the father carried the genes for vermilion eye and forked bristles. Description. — The left side of the gynandromorph is male, with sex-comb and rudimentary fused wing, the left side of the abdomen is male, but the genitalia are female. The ocelli on the head are like those of fused, and the head is therefore male. No sections were made. 50 THE ORIGIN OF GYNANDROMORPHS. Explanations. — An egg containing the rudimentary fused X was fertilized by the vermiHon forked sperm. A paternal vermilion forked X was elim- inated, leaving the other rudimentary fused X to produce the male side, while the female side contains both original X's, namely, rudimentary fused and vermilion forked, and is accordingly wild-type. A /. V f No. 3272. February 10, 1916. C. B. Bridges. Text-figures 36 and 36a (drawings). Parentage. — One X chromosome of the mother carried the genes for sable, garnet and also "sable-duplication" at zero. The other X carried the genes for eosin and for miniature. The father was eosin-miniature. Descriptions. — The entire abdomen was apparently male in shape, banding, and genitalia, though it is not known whether testes or ovaries were present. The right side of the thorax was smaller in size and bore smaller bristles and Text-figuhe 36o. Text-figure 36. Text-figure 37. a smaller (male-type) miniature wing. All right legs were male and both fore- legs bore sex-combs. The right eye (see drawing) had a streak of male tissue ("light" eosin color) running forward completely through. Above and below this streak the tissue was female ("dark" eosin color) There is one other curious feature — the left foreleg as well as the right bore a sex- comb. The head, except the male streak, the right side of the thorax with its miniature wing, and the two rear legs were female Explanations — An egg bearing the eosin miniature non-cross-over X was fertilized by the X sperm carrying eosin and miniature Elimination of one of these X's (either maternal or paternal) was followed by shifting of cleavage nuclei or by shifting of the anlage in the formation of the pupa. THE ORIGIN OF GYNANDROMORPHS. 51 Gynandromorphs Roughly "Fore-and-Aft." No. II 139. January 12, 1914. C. B. Bridges. Text-figure 37 (diagram). Parentage. — The mother was black (second chromosome), but carried only wild-type genes in her X chromosomes. The father was a bar not-])Iack male. Descriptions. — The fly was heterozygous bar in both eyes and female through- out, except for the external genitalia, which were male (penis), and the coloration of abdomen. Sections showed that a pair of ovaries was present. Explanations. — An egg with a wild-type X was fertilized by the X sperm with the gene for bar. Since the male parts did not involve the eye, it can not be determined whether they arose from cells carrying the bar (paternal) or the wild-tj^e (maternal) X. The fly did not show black in the male parts, but since the male region was so small and also normally dark-colored, this case could not be accepted as proving that the elimination did not aff"ect the autosomes, as is proved in several later cases, especially devised for that purpose. or B B No. 1813. July 5, 1915. C. B. Bridges. Text-figure 38 (diagram). Parentage. — One X chromosome of mother carried the genes for forked and for cleft (wing); the other X only wild-type genes. The father was forked. Descriptions. — The head, thorax, wings, and legs were female. The ab- domen had the male coloration and a normal penis. The (poor) sections Text-figure 38. Text-figure 39. Text-figure 40. showed that at least one ovary was present. The wings were not cleft and the male parts showed no forked spines. Explanations.— The egg contained the wild-type X and was fertilizec by the X sperm carrying forked. The paternal X was eliminated, leaving the male parts wild-type. e 52 THE ORIGIN OF GYNANDROMORPHS. No. 2204. October 5, 1914. C. B. Bridges. Text-figure 39 (diagram). Parentage. — One X of the mother carried the gene for eosin, the other the genes for vermihon and forked. The father was bar. Description. — The gynandromorph was of the "fore-and-aft" type. The abdomen was of the male shape, with male coloration on the left side and partially male on the right. There was a normal penis. The eyes were heterozygous bar (female) and the head, thorax, legs, and wing were female. Sections showed that email ovaries were present. Explanations. — Since the male parts were not forked, the egg probably carried the eosin X. The X sperm carried bar. The eyes were female and there is no criterion as to which X was eliminated. An alternative explana- tion assumes a vermihon forked X in the egg, and subsequent elimination of this same X to give the not-forked male parts. No. X. August 1916. A. Weinstein. Text-figure 40 (drawings of wings) . Parentage. — The mother had the genes for eosin, ruby, and forked in one X and for fused in the other. The father was probably eosin ruby forked. Description. — The gynandromorph was largely male anteriorly and female posteriorly. The head was entirely male, with eosin ruby eyes. There were sex-combs on both forelegs, which means that the ventral part of the thorax was male. The left dorsal part was also male, having a small wing which was fused. The right dorsal part was female with a large wild-type wing. The abdomen and genitalia were female. Explanations. — The egg carried a cross-over eosin ruby fused X and the sperm an eosin ruby forked X. Elimination of the paternal X occurred. W rb fu W rb fu w" rtj j No. 4614. January 22, 1918. A. H. Sturtevant. Text-figure 41 (diagram). Parentage. — One X of the mother carried the genes for eosin, vermilion, and forked; the other X carried only wild-type genes. One of the third- chromosomes carried the recessive genes for sepia, spineless, kidney, sooty, and rough; the other was wild-type. The father was a bar male from stock. Description. — Except for the wings, the gynandromorph is divided antero- posteriorly. The right wing was slightly larger than the left and may have been female. The other wing and the remainder of the thorax was male. There were sex-combs on both forelegs. The head was entirely male, with eosin-vermilion eyes and forked bristles. The thorax and legs had also forked bristles. The abdomen was female, both in banding and in shape. The genitalia were female, but slightly abnormal. Tested as a female she proved sterile. None of the third-chromosome recessives showed in any part, either male or female, of the gynandromorphs. Explanations. — An egg containing the non-cross-over eosin vermilion forked X was fertilized by an X sperm carrying bar. The paternal X was eliminated, producing the anterior male parts. The absence of the recessive third-chromo- some characters in the male parts proves that the elimination of the X was independent of the third chromosome. w^ V f vf V f I I I I t I B THE ORIGIN OF GYNANDROMORPHS. 53 Gynandromorphs Produced by XXY Females. No. N 2. December 12, 1912. C. B. Bridges. Plate 3, Figures 1 and la (colored drawings) . Parentage. — The mother was an XXY female homozygous for wliite and heterozygous for the third-chromosome mutant pink. The father was red- eyed, and also heterozygous for pink. Both parents were exceptions produced by secondary non-disjunction. Description. — The fly was a completely bilateral gynandromorph, male on left side, female on right. The male side was smaller, with sex-comb, the genitalia half and half. The fly was unable to breed as a male or as a Text-figure 41. Text-figure 42. Text-figure 43. Text-figure 44. female. The abdomen was large and evidently contained a pair of ovaries The fly was figured in Heredity and Sex, page 163, and the origin given in Journ. Exp. Zool., 1913, page 597. Explanations. — A regular X egg carrying the gene for white was fertilized by an X sperm carrying the wild-type allelomorph red. One of the maternal X's, bearing the gene for white eye, was eliminated. The white-eye character therefore does not appear on either side. As both parents were heterozygous for pink, the fly may have come from third chromosomes bearing normal genes only, or one of them may have had the gene for pink, so that the g>'nan- dromorph is heterozygous. w No. N 3. November 30, 1912. C. B. Bridges. Plate 3, Figures 2 and 2a (colored drawings), (See fig. 17.) Parentage. — The mother was an XXY female, carrj'ing white in both X chromosomes. The father was a wild male. 54 THE ORIGIN OF GYNANDROMORPHS. Description. — The gynandromorph was entirely female, except for the tip of the abdomen below, where a perfectly normal penis and male genitalia were found. The anal prominence and the parts immediately surrounding the genitalia were also male. The posterior ventral plate was male type, being broad, rounded, and hairless. No. 1221. February 2, 1915. C. B. Bridges. Text-figure 42 (diagram). Parentage. — The mother was an XXY wild-type female, one of whose X chromosomes carried the gene for eosin, the other X only wild-type genes. The father was bar. Description. — The gynandromorph was bilateral, except for the head, which was entirely female, with red bar eyes of the heterozygous type. The right side of the thorax dorsally was male, with shorter bristles and very small wing (abnormal). There were no sex-combs. The right side of the abdomen was male in coloration, and the genitalia were almost entirely male. There was a pair of testes with ripe spermatozoa. The two halves of the thorax failed to come together and the male and female parts were unfused. Explanations. — The egg carried the eosin X and may or may not have con- tained a Y. The sperm was the X sperm carrying bar. Elimination of either X occurred. It is possible that the spina bifida condition may have been a result of the gynandromorphism. No. 1892. July 19, 1915. C. B. Bridges. Text-figure 43 (diagram). Parentage. — The mother was a wild-type XXY female, which was an ex- ception from "high" non-disjunction. One X carried the gene for eosin, the other the genes for vermilion and forked. The father was bar. Description. — The fly was female throughout, except that the left side of the abdomen, especially at the tip, showed male coloration and the genitalia were entirely male. The eyes were heterozygous bar (female). Explanation. — An egg with one X (either) and with or without a Y (even chance) was fertilized by an X sperm carrying the gene for bar. Elimination of either X occurred. No. 7673. October 16, 1917. C. B. Bridges. Plate 4, Figure 3 (drawing). Parentage. — The mother was an eosin-eyed XXY exception from a special sttain of "high" non-disjunction (He), which had arisen by equational non- disjunction from the regular high gtj-ain. One of her X chromosomes carried the gene for eosin and the other the genes for eosin and forked. The father was bar. Description. — The male parts of the gynandromorph constituted the entire head, which had eosin eyes of the male type and forked bristles; the left side of the thorax, which had forked bristles, was smaller, with a male-size wing and a sex- comb and a slight patch of male tissue at the tip of the ab- domen, but on the right side, not the left. The abdomen was twisted, as it usually is when bilateral, but since the bristles were not forked, the male parts, if any, must have been below or internal. The right wing was abnormal. Explanations. — An X egg carrying the genes for eosin and forked was fertil- ized by the X sperm carrying the gene for bar. Whether or not a Y was present in the egg is not known (chances even) . Elimination of a paternal bar X occurred. iv^ f to' f I ■ I I B KLAIL 4 GYNANDROMORPHS OF DROSOPHILA THE ORIGIN OF GYNANDROMORPHS. 55 No. 5485. October 18, 1916. C. B. Bridges. Text-figure 44 (diagram). Parentage. — The mother was an XXY female, one of whose chromosomes contained the genes for yellow and for white, the other X the gene for lethal 7. The X chromosome of the father carried the genes for yellow, claret, vermilion, and forked. Description. — The gynandromoi-ph was a yellow female, except that three- quarters of the right eye was white in color and male, the remainder, which was a perfect quarter sector of the eye, being red and female. Sections showed normal ovaries to be present. Explanations. — An egg containing the X chromosome with the genes for yellow and for white was fertihzed by the X sperm with the genes for yellow and the three other recessive genes named above. Elimination of a paternal chromosome occurred, leaving the yellow white X to determine the character of the male parts, viz, the right eye, except for a triangular area of female tissue. y rf V f y w y w Gynandromorphs of Complex Type. No. 487. November 27, 1917. D. E. Lancefield. Text-figure 45 (drawing). Parentage. — The mother was an XXY female homozygous for eosin and miniature. The father was a wild male. Description. — The distribution of male and female parts was very complex. The entire head was female, as evidenced by its large size and by the color of both eyes, which was eosin of the dark female type. The right dorsal part of the thorax was female, as shown by its large size and the large size of the bristles and of the wing, which was also wild-type and not miniature. The only other female parts seemed to be the left ventral part of the thorax, including left legs, since left foreleg carried no sex-comb. The other two sectors of the thorax — the right ventral and the left dorsal — were male, as proved by the smaller size of the parts themselves and of their bristles, and even better by the presence of a sex-comb upon the right foreleg and of a miniature wing of male size upon the left side. As the head was entirely female, the abdomen seemed to be entirely male, except that the armature seemed slightly different in the two sides of the penis. Explanations. — An egg carrying an eosin miniature X (whether or not a Y also is unknown) was fertilized by the X sperm carrying only wild-tyix? genes. Elimination of a paternal X occurred. The segmentation nuclei descended from this same pair of male and female cells were distributed in a regular but complex pattern. No. 941. December 15, 1914. C. B. Bridges. Text-figure 46 (diagram). Parentage. — The parentage is somewhat uncertain, probably as follows: The mother had one X with eosin, notch, tan, and vennilion, and the other X wild-type. The father was eosin tan vermiHon. Description. — The gynandromorph was about half-and-half, but rather complex in the distribution of male and female parts. The head was large, therefore probably female. The eyes were aUke and vermilion. The right wing was a typical notch (female) but was only doubtfully larger than the left. The abdomen was female in coloration anteriorly but male posteriorly. 56 THE ORIGIN OF GYNANDROMORPHS. The genitalia were largely male, but had female parts on the right side. A pair of rudimentary ovaries were present. There were sex-combs on both forelegs, so that the ventral side of the thorax was entirely male. The fly was tan throughout. Explanations. — An egg containing a cross-over chromosome with the genes for notch, tan, and vermilion was fertilized by an X sperm carrying eosin, tan, and vermihon. Elimination of the maternal X was followed by shifting of the cleavage nuclei. N t w" t w^ t No. 983. December 20, 1914. C.B. Bridges. Text-figure 47 (diagram). Parentage. — One of the X chromosomes of the mother carried the genes for white and for bar, and the other X the gene for eosin. The father was miniature. Description. — The separation of the sex-characters is very complex. The dorsal parts of the thorax and the wings are, from their size, female ; the lower Text-figure 45. TEXT-riGURE 46. Text-figure 47. part of the thorax, from the presence of sex-combs on both forelegs, is male. The abdomen is female on the left half and male on the right. The genitalia are female. The abdomen contained a pair of ovaries as seen through the body-wall and in sections. The fly was sterile. The head was entirely male, with white eyes, not-bar. THE ORIGIN OF GYNANDROMORPHS. 57 Explanations. — A cross-over X carrying the gene for white but not for bar was present in the egg, which was fertihzed by the X sperm carrying the gene for miniature. Elimination of this paternal X left a cell with the white X to determine the male parts. In the early cleavage there must have been extensive shifting of the nuclei to produce the observed mosaic of female and male parts. w V m No. 16240521114. Selection Experiment. August 2, 1916. T. H. Morgan. Plate 4, Figure 2 (drawing). Parentage. — The gynandromorph arose in a "selected" notch stock in which the female carried notch in one X and eosin and ruby in the other. The father was eosin ruby. Description. — The gynandromorph was "quartered," being male in the anterior left section and also in the posterior right section, and female in the two other sections. The left eye was mainly eosin ruby, but had a small section of red (female) pushed in from the rear. The left side of the thorax was male, as evidenced by the sex-comb and the shorter wing. The right side of the abdomen had male coloration above and below, and the genitalia were male on the right side and female on the left. The abdomen seemed to have a pair of ovaries when examined, but the sections made later were too poor to confirm this. The right eye was red and the right wing notch. Explanations. — ^An egg carrying the gene for notch was fertilized by a sperm carrying the genes for eosin and ruby. Elimination of the maternal notch X occurred at the first division, leaving the eosin ruby paternal X to determine the character of the male parts. The products of the second division rear- ranged themselves so that sister cells took part in the development of opposite sides of the body. This is only a little more extreme than the usual rear- rangement and shifting of parts (see patch of red in left eye). 10* n w n SPECIAL CASES. The following cases were brought together because they could not be explained simply by the theory of ehmination. Analysis showed that in each of these cases there were present two different chromo- somes, both derived from the mother. Non-disjunction obviously offered an explanation for this fact. But the application of this hypothesis required the additional assumption of "somatic reduction" to explain the gynandromorphism. This means that at an early division the two X's derived from the mother separate without division. On the other hand, if we assume for these cases that both sex chromosomes leave a daughter half at the mid-plate (double elimination) the assump- tion just stated is avoided. Until further explanation is obtained these two interpretations may be given as alternatives. 58 THE ORIGIN OF GYNANDROMORPHS. Doncaster's observations on binucleated eggs of Abraxas, where both nuclei underwent separate reduction and fertihzation, ofifer a simpler explanation. On the other hand, it should be pointed out that there should have been at least as many autosomal mosaics as sex-linked mosaics produced by fertilization of binucleated eggs of heterozygous mothers; and this does not seem to be the case. No. B. 90. June 17, 1912. C. B. Bridges. Text-figure 48 (drawing). Parentage. — This gynandromorph appeared in F2 from the cross of rudimentary female to white miniature male; that is, the mother (F, female) carried rudimentary in one X and white and miniature in the other; and the father was a rudimentary (Fi) male. Description. — The individual seemed to be male through- out. Both eyes were red. Sex-combs were present on both forelegs. The right wing was long, and though slightly deformed, was undoubtedly wild-type. The left wing was a typical and perfect miniature rudimentary wing. The abdomen was entirely male, and when mated to a vermilion female the fly bred as a male, producing abundant offspring. Several pairs of the wild-type daugh- ters and vermilion sons of this mating were bred and all produced red and vermilion in equal numbers, both in males and females. That is, the gynandromorph bred as a wild- type male carrying no mutant genes. Two of the F2 pairs are given as samples: Text-figure 48. Wild-type 9 Wild-type (f Vermilion 9 Vermilion cT B. 98.1 B. 98.2 45 26 33 16 32 30 43 33 The drawing has been previously figured in Zeit. f. ind. Abst. und Verer., 1912, p. 324. Explanations. — Simple elimination fails to explain this case, because the characters of the fly, as well as its genetic behavior, show that it received two different X chromosomes from its mother. For instance, miniature and rudimentary were both present in the left (male) wing, which proves that the X contained in these parts came from the mother and that crossing-over in the mother must have occurred. Since the right wing was wild-type, its cells must have contained a wild-type X, which likewise could only have come from the mother. The Fi and F2 offspring of the gynandromorph showed that he had such a wild-type X in the testis, which presumably came from the same kind of cells as those of the right side. The offspring also show that the gynandromorph had not received an X sperm from the father, which would have given rudimentary offspring. Therefore the right side, at least, must have come from a Y-bearing sperm, as further proved by the fact that the gynandromorph was fertile as a male (males without a Y being sterile). On the view that the gynandromorph came from an egg with two nuclei, a simple explanation of the result may be given. Before reduction, each of the postulated nuclei must have had one white miniature X and one red rudimentary X chromosome; after crossing-over and reduction in each, one THE ORIGIN OF GYNANDROMORPHS. 59 nucleus contained a white miniature rudimentary cross-over X, and the other nucleus a wild-t>i^e cross-over X. Each nucleus was fertilized by a Y-type sperm, proof of which for the right side has been given; proof for "left side is as follows: The left wing is miniature as well a* rudimentary, and since Text-figure 49. Text-figure 50. Text-figure 51. the X of the father did not carry miniature, this left side could not have contained a paternal X and must therefore have contained a paternal Y chromosome. One of the cross-over chromosomes was white as well as miniature and rudimentary; but since the eye on the side with miniature was red, we may suppose that all of the head came, as is very often the case, from cells from one side only, namely, the right, which was here carrying red; or this cross- over chromosome may have come from double crossing-over, and in this case it would have carried red. Lejl side. Right side. W m VI or On an alternative view that both of these X's were in a single nucleus, the following assumption seems necessary. An XX egg was produced by reduc- tional primary non-disjunction (see Bridges, 1916), preceded by crossing-over, so that one X contained white miniature rudimentary and the other was the complementary X containing only wild-type genes. This XX egg wa:? then fertilized by a Y sperm. That the individual was entirely male with no female parts can be explained either by double elimination or somatic reduction at the first division of the zygote; that is, one member of each pair was caught by the elimination plate, 60 THE ORIGIN OF GYNANDROMORPHS. SO that each of the two first daughter cells had but one X and these different from each other. Zygote. Left side. Right side. w m r w m r ■ I I III 1 X ! X Y No. I 92. August 16, 1913. C. B. Bridges. Text-figure 49 (diagram). Parentage. — One of the X chromosomes of the mother carried the genes for vermiHon and for fused and the other X the gene for bar. The father was vermilion fused. Description. — The gynandromorph was completely bilateral, except for the genitalia, which were female. The left side was male, as evidenced by the smaller size throughout, by the sex-comb, and by male coloration on the abdomen. The left eye was bar of the male type. The right side was female in every part, and was chiefly remarkable in that its large wing was fused. The eyes were both red, not vermilion. The right eye was round, not hetero- zygous bar. A pair of ovaries was found in the sections. Explanations. — On the assumption of two nuclei in the egg, one nucleus after reduction contained a non-cross-over bar X chromosome, and this nucleus fertilized by a Y sperm gave the bar male left side, with bar eye; the other nucleus after crossing-over and reduction contained a cross-over fused X chromosome, wh ch nucleus fertilized by the vermilion fused X spenn gave the female right side with fused wing: Left side. Right side. B fu On the alternative view that both X's from the mother were retained after reduction in the same nucleus of the egg, the case is difficult, but may be accounted for in the following way: Since the left side is male throughout and shows the bar eye-character (of male type), this side must have come from a non-cross-over X of the mother. But this bar X is not represented at all on the right side, as proved by the round eye, which, although female, is not even heterozygous for bar. That the right side is female requires that two X's be present, and the fact that the wing is fused requires that both carry the fused gene. A non-cross-over vermilion fused X must have come from the mother along with the bar X. The egg, then, was an XX egg pro- duced by primary non-disjunction which was equational, since the bar X was a non-cross-over and the fused X a cross-over chromosome (Bridges, 1916). This XX egg was fertilized by an X sperm carrying the genes for vermilion and for fused. It is known that XXX zygotes are unable to hatch as adult flies (Bridges, 1916), but since neither the time nor the mechan- ism of their elimination is known, it is possible that if double elimination or somatic reduction followed soon after fertilization the life of the XXX individual would be saved, hut at the price of becoming a gynandromorph. Two of the X's, in this case the paternal vermilion fused and the maternal THE ORIGIN OF GYNANDROMORPHS. 61 fused cross-over X, remained in one cleavage cell which gave rise to the not- vermilion not-bar fused female right side. The other X, the maternal non- cross-over bar X, passed into the other daughter cell and gave rise to the not-vermilion bar not-fused left side. - Zygote. Left side. Right side. V fu V Ju • 1 ^" B B No. 937. December 17, 1914. C. B. Bridges. Text-figure 50 (diagram). Parentage. — The grandmother was a wild-type XXY female carrying the genes for eosin and vermilion in one X and in the other only wild-type genes; the grandfather was white bar. By equational non-disjunction an XXY eosin daughter was produced which carried eosin and vermilion in one X and eosin in the other. This female was out-crossed to a vermilion male and produced among the sons a mosaic. Description. — The mosaic, as in the case B 90, was male throughout, but the left eye was eosin (of the male type) and the right eye was eosin vermilion. The male was fertile when bred to a vermilion female, giving wild-type daughters and vermilion sons (No. 1116). One of the wild-type daughters out-crossed to a forked male gave eosin and vermilion as the main classes of the sons. Explanations. — On the hypothesis of a binucleated egg, one nucleus after reduction contained an eosin vermilion X and the other nucleus an eosin X. Since no eye-color corresponded to the X sperm of the father, and since the individual was male throughout, both of the egg-nuclei must have been fert lized by a Y sperm, which is further shown by the fertility of the male. Left side. Right side. On the view that a single nucleus was present, the following situation de- velops: Since the right eye showed both eosin and vermilion, the mosaic must have contained the eosin vermilion X of the mother. Since the other eye showed eosin (not vermilion), this X must have been the other or eosin X of the mother. That is, both X chromosomes of the mosaic came from the mother by means of an XX egg produced through non-disjunction. The ver- milion X of the father was not present at all, as proved by the fact that the left eye of the mosaic was eosin (not red) and male (not female), and by the breeding-test, which showed that the gonads carried only the eosin X. The sperm was not the X sperm of the father, but the Y sperm, as further indicated by the fertility of the male. As in case B 90, there must have been double elimination or somatic re- duction, so that one cleavage-cell received the eosin X and a Y, and the other 62 THE ORIGIN OF GYNANDROMORPHS. the eosin vermilion X and a Y. The gonads developed from an eosin cell as shown by the Fj and F2 results of his breeding test. Zygote. Left bide. Right side. w* w^ No. 1333. February 19, 1915. C. B. Bridges. Text-figure 51 (diagram). Parentage. — The mother was a wild-type XXY female, carrying the genes for eosin in one X and for vermilion and forked in the other. The father was bar. Description. — The fly was female throughout, except for the left eye which was round (not bar) and red (not eosin or vermilion). The eye has been examined repeatedly at different times since the mosaic was on hand, and the eye is undoubtedly not-bar and is of the right size for a male. The right eye was heterozygous bar. There were no forked bristles present around the left eye elsewhere. The female was mated to a sable forked male and pro- duced: No. 1555 — forked females, 11; forked bar females, 0; bar females, 18; wild-type female, 1; vermilion forked males, 18; bar males, 6; vermilion bar males, 3; forked males, 2. Explanations. — On the hypothesis of a binucleated egg, one nucleus after reduction contained a cross-over wild-type X and the other a non-cross-over vermilion forked X chromosome. The former fertilized by a Y sperm gave rise to the wild-type (male) left eye; the latter fertilized by a bar X sperm gave rise to the rest of the fly. Lejt side. Right side. V f B The following alternative possibilities may be considered: The simplest possible explanation is that this is a mosaic or somatic mutation — that the bar gene in the cell that gave rise to the left eye reverted to not-bar, or to an allelomorph which gives a small round eye. If, as is more probable, this mosaic is a gynandromorph arising by chromosomal disturbance, the ex- planation is like that for No. I 92, i. e., the egg arose by equational non-dis- junction and contained a non-cross-over vermilion forked X and a cross-over wild-type X. This egg probably did not contain a Y, as evidenced by the lack of exceptions among the sons of the mosaic, and as is possible in accordance with the assumption of equational non-disjunction, for equational non-dis- junction, even when occurring in a female with a Y, is probably always primary. One eye was clearly heterozygous bar; hence it is known that the XX egg was fertilized by an X sperm carrying the gene for bar. This XXX zygote would ultimately die, unless at an early stage the XXX condition was cor- rected by reduction or elimination. Double elimination or somatic reduction in a cleavage-cell would save the individual, but turn it into a gynandromorph. The other X chromosome, wild-type, passed into the sister cell and gave rise THE ORIGIN OF GYNANDROMORPHS. 63 to male parts, which, because of the lateness of the occurrence, or from shift- ing of nuclei, constituted but a small part of the gynandromorph. Zygote. V 1 / 1 X X X Left side. X liiyhl side. f 1 1 X X B B No. 2349. November 3. 1915. C. B. Bridges. Text-figure 52 (drawing). Parentage. — The mother was from a strain of high non-