True Parthenogenesis Research Articles

True Parthenogenesis and Female-Biased Sex Ratios in Cicadomorpha and Fulgoromorpha (Hemiptera, Auchenorrhyncha).

Insects are renowned for their remarkable diversity of reproductive modes. Among these, the largest non-holometabolous order, Hemiptera, stands out with one of the most diversified arrays of parthenogenesis modes observed among insects. Although there are extensive reviews on reproduction without fertilization in some hemipteran higher taxa, no such analysis has been conducted for the large suborders Fulgoromorpha (planthoppers) and Cicadomorpha (leafhoppers). In both groups, there are species that reproduce by true parthenogenesis, specifically thelytoky, and in Fulgoromorpha, there are species that reproduce by pseudogamy or, more specifically, sperm-dependent parthenogenesis. In this review paper, we give and discuss the only currently known examples of true parthenogenesis in Fulgoromorpha and Cicadomorpha, mainly from the planthopper family Delphacidae and the leafhopper family Cicadellidae. We analyze patterns of distribution, ecology, mating behavior, acoustic communication, and cytogenetic and genetic diversity of parthenoforms and discuss hypotheses about the origin of parthenogenesis in each case. We also highlight examples in which natural populations show a shift in sex ratio toward females and discuss possible causes of this phenomenon, primarily the influence of endosymbiotic bacteria capable of altering the reproductive strategies of the hosts. Our review is mainly based on studies in which the authors have participated.

Species Distribution Models and Niche Partitioning among Unisexual Darevskia dahli and Its Parental Bisexual (D. portschinskii, D. mixta) Rock Lizards in the Caucasus

Among vertebrates, true parthenogenesis is known only in reptiles. Parthenogenetic lizards of the genus Darevskia emerged as a result of the hybridization of bisexual parental species. However, uncertainty remains about the mechanisms of the co-existence of these forms. The geographical parthenogenesis hypothesis suggests that unisexual forms can co-exist with their parental species in the “marginal” habitats. Our goal is to investigate the influence of environmental factors on the formation of ecological niches and the distribution of lizards. For this reason, we created models of species distribution and ecological niches to predict the potential geographical distribution of the parthenogenetic and its parental species. We also estimated the realized niches breadth, their overlap, similarities, and shifts in the entire space of predictor variables. We found that the centroids of the niches of the three studied lizards were located in the mountain forests. The “maternal” species D. mixta prefers forest habitats located at high elevations, “paternal” species D. portschinskii commonly occurs in arid and shrub habitats of the lower belt of mountain forests, and D. dahli occupies substantially an intermediate or “marginal” position along environmental gradients relative to that of its parental species. Our results evidence that geographical parthenogenesis partially explains the co-existence of the lizards.

Not always young: The first vertebrate ancient origin of true parthenogenesis found in an Amazon leaf litter lizard with evidence of mitochondrial haplotypes surfing on the wave of a range expansion

In vertebrates, true parthenogenesis is found only in squamate reptiles and (mostly) originates via interspecific hybridization after secondary contact. In many cases, parthenogenesis is followed by an increase of ploidy, resulting in triploid lineages. Phylogenetic analyses derived from nuclear and maternally inherited markers can help to clarify the mechanisms of origin and the potential parental species involved. In the Amazon region, parthenogenetic lizards of the Loxopholis percarinatum complex are widely distributed, comprising both diploid and triploid clones. Recently, putative males of L. percarinatum were reported, suggesting the existence of bisexual populations based on morphological data. Here, we used mitochondrial and nuclear data to investigate the origin of parthenogenesis in Loxopholis. Mitochondrial DNA analysis revealed three major lineages: unisexual/2n, unisexual/3n and bisexual, the last of which comprised two sub-lineages placed as the sister taxon to the unisexual/3n lineage. Genetic divergence among the lineages was ∼10% but was lower between the unisexual/3n and bisexual lineages (∼6%). Both mtDNA and nuDNA indicated that individuals from the bisexual lineages might belong to a new species. Nuclear DNA evidence indicates that crossings occasionally occur between unisexual 2n and males from the new bisexual species. Phylogenetic analysis of nuDNA showed L. ferreirai as the closest described bisexual species to the complex. Our results revealed an ancient origin of parthenogenesis in the L. percarinatum complex, in contrast to most young (Pleistocene) parthenogenetic lizards described thus far. Two hybridization events seem to have been involved: the first event occurred in late Miocene, between the ancestral lineage (“A”) of the new bisexual species (as a maternal species) and the ancestral lineage of L. ferreirai, as a paternal species of L. percarinatum 2n; and the second event occurred in Pliocene-Pleistocene, in a backcross between L. percarinatum 2n and a male from the common ancestor (“B”) of the new bisexual species giving rise to the lineage of L. percarinatum 3n. With these results, we showed that L. percarinatum complex also includes, at least, one undescribed bisexual species in addition to the two known parthenogenetic lineages (2n and 3n). Finally, we present evidence that diploid individuals of L. percarinatum experienced an event of wide demographic expansion over the past million years under an allele surfing model.

The origin of multiple clones in the parthenogenetic lizard species Darevskia rostombekowi.

The all-female Caucasian rock lizard Darevskia rostombekowi and other unisexual species of this genus reproduce normally via true parthenogenesis. Typically, diploid parthenogenetic reptiles exhibit some amount of clonal diversity. However, allozyme data from D. rostombekowi have suggested that this species consists of a single clone. Herein, we test this hypothesis by evaluating variation at three variable microsatellite loci for 42 specimens of D. rostombekowi from four populations in Armenia. Analyses based on single nucleotide polymorphisms of each locus reveal five genotypes or presumptive clones in this species. All individuals are heterozygous at the loci. The major clone occurs in 24 individuals and involves three populations. Four rare clones involve one or several individuals from one or two populations. Most variation owes to parent-specific single nucleotide polymorphisms, which occur as heterozygotes. This result fails to reject the hypothesis of a single hybridization founder event that resulted in the initial formation of one major clone. The other clones appear to have originated via post-formation microsatellite mutations of the major clone.

Clonal diversity and clone formation in the parthenogenetic Caucasian rock Lizard Darevskia dahli [corrected

The all-female Caucasian rock lizard species Darevskia dahli and other parthenogenetic species of this genus reproduce normally via true parthenogenesis. Previously, the genetic diversity of this species was analyzed using allozymes, mitochondrial DNA, and DNA fingerprint markers. In the present study, variation at three microsatellite loci was studied in 111 specimens of D. dahli from five populations from Armenia, and new information regarding clonal diversity and clone formation in D. dahli was obtained that suggests a multiple hybridization origin. All individuals but one were heterozygous at the loci studied. Based on specific allele combinations, 11 genotypes were identified among the individuals studied. Individuals with the same genotypes formed distinct clonal lineages: one major clone was represented by 72 individuals, an intermediate clone was represented by 21 individuals, and nine other clones were rare and represented by one or several individuals. A new approach based on the detection and comparison of genotype-specific markers formed by combinations of parental-specific markers was developed and used to identify at least three hybridization founder events that resulted in the initial formation of one major and two rare clones. All other clones, including the intermediate and seven rare clones, probably arose through postformation microsatellite mutations of the major clone. This approach can be used to identify hybridization founder events and to study clone formation in other unisexual taxa.

Clonal Diversity and Clone Formation in the Parthenogenetic Caucasian Rock Lizard Darevskia dahli

The all-female Caucasian rock lizard species Darevskia dahli and other parthenogenetic species of this genus reproduce normally via true parthenogenesis. Previously, the genetic diversity of this species was analyzed using allozymes, mitochondrial DNA, and DNA fingerprint markers. In the present study, variation at three microsatellite loci was studied in 111 specimens of D. dahli from five populations from Armenia, and new information regarding clonal diversity and clone formation in D. dahli was obtained that suggests a multiple hybridization origin. All individuals but one were heterozygous at the loci studied. Based on specific allele combinations, 11 genotypes were identified among the individuals studied. Individuals with the same genotypes formed distinct clonal lineages: one major clone was represented by 72 individuals, an intermediate clone was represented by 21 individuals, and nine other clones were rare and represented by one or several individuals. A new approach based on the detection and comparison of genotype-specific markers formed by combinations of parental-specific markers was developed and used to identify at least three hybridization founder events that resulted in the initial formation of one major and two rare clones. All other clones, including the intermediate and seven rare clones, probably arose through postformation microsatellite mutations of the major clone. This approach can be used to identify hybridization founder events and to study clone formation in other unisexual taxa.

Phylogenetic Insights on Evolutionary Novelties in Lizards and Snakes: Sex, Birth, Bodies, Niches, and Venom

Squamate reptiles (lizards and snakes) are a diverse clade in which there appear to have been multiple origins of many remarkable traits, including (a) parthenogenetic reproduction, (b) viviparity, (c) snake-like, limb-reduced body form, (d) herbivory, and (e) venom. These repeated transitions make squamates an outstanding/excellent system for addressing many fundamental questions in evolutionary biology. For example, they are the only vertebrate group with true parthenogenesis (with at least 40 separate origins), they have more origins of viviparity than any other group of vertebrates, and they have undergone dramatic changes in body form (lizard-like to snake-like) dozens of times. New molecular phylogenies for squamates have overturned many traditional hypotheses and taxonomies based on morphology and are now revealing exciting new insights into the evolution of many of these traits at both higher and lower taxonomic levels. In this review, we summarize many of these new insights and outline important areas for future research.

DNA EVIDENCE FOR NONHYBRID ORIGINS OF PARTHENOGENESIS IN NATURAL POPULATIONS OF VERTEBRATES

Naturally occurring unisexual reproduction has been documented in less than 0.1% of all vertebrate species. Among vertebrates, true parthenogenesis is known only in squamate reptiles. In all vertebrate cases that have been carefully studied, the clonal or hemiclonal taxa have originated through hybridization between closely related sexual species. In contrast, parthenogenetic reproduction has arisen in invertebrates by a variety of mechanisms, including likely cases of "spontaneous" (nonhybrid) origin, a situation not currently documented in natural populations of vertebrates. Here, we present molecular data from the Neotropical night lizard genus Lepidophyma that provides evidence of independent nonhybrid origins for diploid unisexual populations of two species from Costa Rica and Panama. Our mitochondrial and nuclear phylogenies are congruent with respect to the unisexual taxa. Based on 14 microsatellite loci, heterozygosity (expected from a hybrid origin) is low in Lepidophyma reticulatum and completely absent in unisexual L. flavimaculatum. The unique value of this system will allow direct comparative studies between parthenogenetic and sexual lineages in vertebrates, with an enormous potential for this species to be a model system for understanding the mechanisms of nonhybrid parthenogenesis.

Genetic Variation and De Novo Mutations in the Parthenogenetic Caucasian Rock Lizard Darevskia unisexualis

Unisexual all-female lizards of the genus Darevskia that are well adapted to various habitats are known to reproduce normally by true parthenogenesis. Although they consist of unisexual lineages and lack effective genetic recombination, they are characterized by some level of genetic polymorphism. To reveal the mutational contribution to overall genetic variability, the most straightforward and conclusive way is the direct detection of mutation events in pedigree genotyping. Earlier we selected from genomic library of D. unisexualis two polymorphic microsatellite containg loci Du281 and Du215. In this study, these two loci were analyzed to detect possible de novo mutations in 168 parthenogenetic offspring of 49 D. unisexualis mothers and in 147 offspring of 50 D. armeniaca mothers . No mutant alleles were detected in D. armeniaca offspring at both loci, and in D. unisexualis offspring at the Du215 locus. There were a total of seven mutational events in the germ lines of four of the 49 D. unisexualis mothers at the Du281 locus, yielding the mutation rate of 0.1428 events per germ line tissue. Sequencing of the mutant alleles has shown that most mutations occur via deletion or insertion of single microsatellite repeat being identical in all offspring of the family. This indicates that such mutations emerge at the early stages of embryogenesis. In this study we characterized single highly unstable (GATA)n containing locus in parthenogenetic lizard species D. unisexualis. Besides, we characterized various types of mutant alleles of this locus found in the D. unisexualis offspring of the first generation. Our data has shown that microsatellite mutations at highly unstable loci can make a significant contribution to population variability of parthenogenetic lizards.

Making it on their own: sperm-dependent hybrid fishes (Cobitis) switch the sexual hosts and expand beyond the ranges of their original sperm donors

Interspecific hybridization may result in asexual hybrid lineages that reproduce via parthenogenesis. Contrary to true parthenogens, sperm-dependent asexuals (gynogens and hybridogens) are restricted to the range of bisexual species, generally the parental taxa, by their need for a sperm donor. It has been documented that asexual lineages may rarely use sperm from a non-parental species or even switch a host. The available literature reports do not allow distinguishing, between whether such host switches arise by the expansion of asexuals out of their parental's range (and into that of another's) or by the local extinction of a parental population followed by a host switch. The present study combines new and previously collected data on the distribution and history of gynogenetic spined loaches (Cobitis) of hybrid origin. We identified at least three clonal lineages that have independently switched their sperm dependency to different non-parental Cobitis species, and in cases incorporated their genomes. Our current knowledge of European Cobitis species and their hybrids suggests that this pattern most probably results from the expansion of gynogenetic lineages into new areas. Such expansion was independent of the original parental species. This suggests that sperm dependence is not as restrictive to geographical expansion when compared with true parthenogenesis as previously thought.

Amazon mollies

Amazon mollies

True parthenogenesis induction or successful feminization?

When transmitted by female hosts only, endosymbionts are subject to sex-biased selective pressures: the effect that they have on male hosts does not affect their own fitness. The endocellular bacterium Wolbachia wonderfully illustrates the possible evolutionary outcomes of this situation: it has evolved various systems allowing itself to invade host populations by favoring the production of infected females, regardless of possible detrimental effects to infected males. Wolbachia belongs to the α-group of proteobacteria, which includes numerous endosymbionts, the most famous of which is probably mitochondria. The Cytophaga-Flexibacter-Bacteroid (CFB) group is much less known for its reproductive parasites, but this is about to change [1].

Evolutionary genetics and ecology of sperm‐dependent parthenogenesis

AbstractSperm‐dependent (or pseudogamous) forms of parthenogenetic reproduction occur in a wide variety of animals. Inheritance is typically clonal and matroclinous (of female descent), but sperm are needed to initiate normal development. As opposed to true parthenogenesis (i.e., sperm‐independent reproduction), pseudogamous parthenogenetic lineages must coexist with a ‘sperm donor’— e.g., males from a conspecific sexual lineage, conspecific hermaphrodites, or males from a closely related sexual species. Such sperm donors do not contribute genetically to the next generation. The parasitic nature of sperm‐dependent parthenogenesis raises numerous ecological and evolutionary questions. How do they arise? What factors help stabilize coexistence between the pseudogamous parthenogens and their sperm donors (i.e., ‘sexual hosts’)? Why do males waste sperm on the asexual females? Why does true parthenogenesis not evolve in pseudogamous lineages and free them from their dependency on sperm donors? Does pseudogamous parthenogenesis provide compensatory benefits that outweigh the constraints of sperm‐dependence? Herein, we consider some genetic, ecological, and geographical consequences of sperm‐dependent parthenogenesis in animals.

The Caucasian rock lizard Lacerta rostombekovi: a monoclonal parthenogenetic vertebrate

Among vertebrates, true parthenogenesis (self-perpetuating all-female species) occurs only in reptiles; these species are of hybrid origin. To date, all diploid parthenogenetic reptiles examined exhibit some genetic diversity, resulting in the existence of more than one clone. The sole exception to this is the Caucasian rock lizard Lacerta rostombekovi, which appears to consist of only a single clone.

Thelytoky in Taeniogonalos venatoria Riek (Hymenoptera: Trigonalyidae), with Notes on its Distribution and First Description of Males

ABSTRACTThe Trigonalyidae, which have previously been thought to reproduce arrhenotokously like most parasitic Hymenoptera, are added to the list of families from which thelytoky (true parthenogenesis) is recorded. This has been inferred for Taeniogonalos venatoria Riek on the basis of a male:female sex ratio in the field ranging from about 1:250 to 0:1500. The rare male of this species is described for the first time, and the known distribution of the species extended to include South Australia. The host range of T. venatoria, which parasitises widely dispersing pergid sawfly larvae, is proposed as a possible reason for its thelytokous mode of reproduction.

1 Cytoskeleton, Cellular Signals, and Cytoplasmic Localization in Chaetopterus Embryos

Publisher Summary The use of Chaetopterus as a system for study in developmental biology began with E. B. Wilson, who briefly described its early development along with that of several other annelids. Experimental analysis of the development of this organism began with Jacques Loeb in a paper in which he misdescribed “differentiation without cleavage” resulting from K + activation as true parthenogenesis. Experimental studies of the development of Chaetopterus have emphasized three areas: the regulation of the cell cycle [germinal vesicle break-down (GVBD)], mechanisms of fertilization and egg activation, and the effects of egg organization on development. Although this chapter stresses the last area, it briefly mentions the advantages of Chaetopterus oocytes and eggs for the first two areas. The unique feature that makes Chaetopterus of particular interest for studies of egg and embryo organization in development is the ability of the artificially activated or fertilized egg to undergo differentiation without cleavage. Artificial activation can be induced by excess KCl. Differentiation without cleavage also occurs in fertilized eggs subjected to temporary cleavage inhibition by treatment with cytochalasin B and in polyspermic embryos. This interesting phenomenon is discussed in the chapter.

Can Parthenogenetic Cnemidophorus laredoensis (Teiidae) Coexist with Its Bisexual Congeners?

-Wright and Lowe (1968) and Cuellar (1977) suggested that parthenogenetic Cnemidophorus can survive only in isolation from their bisexual congeners because the latter would otherwise eliminate the parthenoforms through competition and/or hybridization. Data from studies of the parthenogenetic clone LAR-A of the Cnemidophorus laredoensis subgroup suggest this hypothesis is not correct. The bisexual species C. gularis occurs at 24 of the 39 sites at which LAR-A has been found, and neither form is consistently more abundant than the other at syntopic sites. The literature documents many cases where parthenogenetic whiptails coexist with their bisexual congeners, suggesting parthenoforms do not require isolation as previously believed. One of two things must be happening to allow parthenoforms to coexist with bisexuals: (1) competition and do not occur; or (2) these processes do occur but some other factor counteracts their effect. At present, too little data exist to evaluate which of these alternatives is correct. However, analysis of lizard diets at three sites of syntopy and data reported in studies of other parthenoforms are used to advance testable hypotheses in the hope of stimulating future research. The lizard genus Cnemidophorus (Teiidae) includes several forms that reproduce by true parthenogenesis in addition to many bisexual species. The parthenoforms originate as hybrids between bisexual species; the hybrids then reproduce asexually to generate clones of genetically identical individuals (Wright, 1978; Cole, 1979). The existence of parthenoforms presents biologists with an interesting evolutionary problem: how do such forms persist in a world dominated by sexually reproducing species that are presumably better adapted to the environment through natural selection? In their classic paper, Wright and Lowe (1968) proposed the weed hypothesis, which states that parthenogenetic whiptails can become established only in disturbed, marginal, or ecotonal habitats because such habitats are unsuitable for bisexual whiptails. A slightly different view was proposed by Cuellar (1977) who suggested parthenogenetic whiptails occupy only floodplain, beach, or lakeside habitats because parthenoforms can rapidly colonize areas where natural disasters periodically eliminate lizard populations, and because bisexual species are usually absent from such habitats. The implication of both hypotheses is that parthenoforms are poor competitors, presumably because their limited genotypic diversity translates into narrow ecological breadth (Bell, 1982; Case and Taper, 1986). Therefore parthenoforms can avoid competitive exclusion by their bisexual congeners only by occupying disturbed habitats. Cuellar (1977) also emphasized that isolation from bisexual forms ensures that a parthenoform will not lose its genetic identity through hybridization, a phenomenon termed destabilizing hybridization by Lynch (1984). This occurs if diploid parthenoforms mate with males of bisexual species to produce triploid hybrids that are either sterile or are parthenogenetic themselves (Lynch, 1984; Vrijenhoek, 1989). The latter case should lead to the replacement of diploid parthenoforms by triploid parthenoforms. Hybridization with bisexual species might also be detrimental to a parthenoform if the fertilization of a parthenogenetic egg caused the egg to fail to develop, resulting in waste of reproductive effort (White and Contreras, 1979). Both Wright and Lowe (1968) and Cuellar (1977) suggested that parthenoforms should rarely be found at site where bisexual species occur, and in those ra e instances where the two forms do co-occur, the bisexual species should be rare enough that it does not exert a strong impact on the parthenoform. However, these hypotheses have not been tested rigorously. The parthenogenetic Cnemidophorus laredoensis subgroup comprises several allodiploid clones that occupy a narrow zone on either side of the Rio Grande from Del Rio (Val Verde County), Texas, to within 16 km of the Gulf of Mexico (Walker, 1987a, b). The subject of this paper is the clone LAR-A, (originally described as Cnemidophorus laredoensis by McKinney et al., 1973). A second major clone, named LAR-B, discovThis content downloaded from 207.46.13.160 on Mon, 17 Oct 2016 05:18:30 UTC All use subject to http://about.jstor.org/terms M. A. PAULISSEN ET AL. TABLE 1. Snout-vent lengths (SVL) and mass of LAR-A and C. gularis at three sites in Texas. Values are mean + standard deviation, sample sizes are given in parentheses. Statistically significant differences, as evaluated by Mann-Whitney U tests, are indicated by an asterisk. The sample sizes for SVL and mass at Garceno differ because lizards were not weighed during the 1 May collection.

On the cytology of apogamy and apospory.—II. Preliminary note on apospory

Apospory is the direct vegetative process which leads from the sporophyte to the gametophyte without the intervention of spores. This phenomenon has for a long time been known to occur in mosses and ferns, and several writers have described its morphological characters, but its cytological history has hitherto remained unrecorded. In a previous note the cellular features of apogamy were briefly described, and it is here proposed to treat the problem of apospory in a similar manner. The following remarks are limited to the study of apospory in Nephrodium pseudo-mas Rich. var. cristata apospora , Druery, but it is of interest to note that within the limits of a (probably) single, but highly variable species, almost all grades of apospory and apogamy, with the exception of true parthenogenesis, have been encountered. Our thanks are especially due to Mr. C. T. Druery, who has kindly supplied us with the original fronds, and to the Curator of the Chelsea Physic Garden, who has most carefully cultivated the plants with excellent results. The aposporal character of Nephrodium pseudo-mas var. cristata apospora appears to have been first noted by Dr. F. W. Stansfield. It occurred as a sport in a very damp fernery. Our fronds were pegged down in pans of moist earth, and the cultures have been grown in a greenhouse kept at an average temperature of 55º to 60º Fahr. in the winter and of 65º to 70º Fahr. in the summer. It was found that no aposporous growths appear until the fronds have been pegged down, and in each case the fronds were severed from the plant, as this was found to greatly encourage the production of the growths. The aposporous growth is rapid and prolific; fronds treated during the spring and summer showe prothalli, bearing embryos, in three weeks' time. By the autumn these young plants were sufficiently matured to have their leaves layered, and these shortly exhibited the same characteristic feature. It is immaterial as to which surface of the frond is in contact with the soil. So far as has been ascertained this fern remains very constant in character, and continues to breed true. In the plants grown at Chelsea, no trace of a sporangium or sorus has appeared on any of the leaves.

Parthenogenesis in the Coleoptera

IN the “concluding remarks” in his treatise on “Wahre Parthenogenesis” (1856), von Siebold says, “Es ist daher jetzt Aufgabe der Entomologen, nach weiteren Beispielen von Parthenogenesis in der Insektenwelt zu forschen”; and on the last page (237) of his “Beitrage zur Parthenogenesis,” published fifteen years later, he expresses the conviction that many facts relating to this phenomenon are still to be discovered. The instances of true parthenogenesis discussed or referred to in these two works relate to insects of the orders Hymenoptera and Lepidoptera, and to some crustaceans. Including viviparous agamogenesis, however, as parthenogenetic, the orders Hemiptera and Diptera also furnish examples of this mode of reproduction; and for its occurrence in at least one genus of the Trichoptera I have the authority of Mr. R. McLachlan, F.R.S. The possibility of parthenogenetic reproduction in the Coleoptera rests only, so far as I am aware—see “Comparative Embryology,” by F. M. Balfour, vol. i. p. 64—on the single instance communicated by me to this journal last year (Nature, vol. xx. p. 430), and this being so, it seemed desirable to make sure of this point by further research during the season now almost past. Accordingly I have this year kept a considerable number of females of Gastrophysa raphani, laying unimpregnated eggs, and with results which have not only confirmed the previous experience, but much extended it, as I am at present in possession of a living beetle reared from a parthenogenetic ovum. With your permission I shall now endeavour as briefly as possible to give those circumstantial details without which a bald statement of results would not carry with it a rational conviction of the accuracy of my observations.

Siebold's New Researches in Parthenogenesis*

A MIDST the all-absorbing discussion of the problems which have arisen out of the general acceptance among biologists of the law of evolution, the phenomenon of Parthenogenesis which, previously to Mr. Darwin's work on the Origin of Species, excited the interest and called forth the investigations of observers in much the same manner as his theory has done of late years, has met with a reverse of fortune and fallen into a subordinate rank of popularity. The distinguished naturalist, however, who fifteen years ago gave so stunning a blow to current theories of the reproductive process, by demonstrating the occurrence in moths and bees of what he designated as “true parthenogenesis ”—that is to say, the development, without impregnation, of an ovum capable of being impregnated—has not let the subject drop. Professor Siebold has made further experimental researches, establishing again, and on a larger basis, his former conclusion, and adding at least one new fact of great general importance for the understanding of the process of sexual reproduction. Although upon its first appearance in 1856, the conclusion arrived at in his “Wahre Parthenogenesis” was admitted by almost all competent naturalists to be thoroughly demonstrated, and beyond the reach of criticism; yet some more and some less eminent biologists have not been wanting to deny the Lucina sine concubitu, and have raised such objections as that of a possible error in the condition of the experiments depending on the exclusion of males from the supposed parthenogenetic female; and again, that these so-called females were not demonstrated 'not to be hermaphrodites.” Indeed so deeply rooted is the conviction that eggs are made to be impregnated by spermatozoa, and that they then, and then only, can proceed to develop, that Siebold felt it necessary to add to his proofs, in order to establish his position that not only do unimpregnated eggs develop into perfect animals, but that such an event is by no means an exceptional occurrence among certain groups, and has a definitely fixed and orderly recurrence amongst them. He naturally was also anxious to extend the class-limits within which a true parthenogenesis can be said to occur, and he desired to inquire into the sex of the parthenoge-netically-produced offspring in such cases as could be critically and decisively studied. Hence the renewed researches which have extended over several years, and the results of which are given in the present brochure.