A radiation analysis of a comstockiella chromosome system: destruction of heterochromatic chromosomes during spermatogenesis in Parlatoria oleae (Coccoidea: Diaspididae)

In the males of the olive scale insect, Parlatoria oleae (2n=8), the paternal set of chromosomes becomes heterochromatic during late cleavage or early blastula and remains so until spermatogenesis. Immediately before the onset of meiosis in the males one or more heterochromatic chromosomes disappear from each primary spermatocyte. At prophase four euchromatic and from one to three heterochromatic chromosomes are present in each cell. The disappearance of the heterochromatic chromosomes before meiosis could be due either to the dehetero-chromatization of the heterochromatic chromosomes and their subsequent pairing with their euchromatic homologues, or to the destruction of the heterochromatic chromosomes. — The alternative interpretations of spermatogenesis in P. oleae were tested by using chromosome aberrations, which had been induced in the heterochromatic set by paternal X-irradiation, as genetic markers in breeding tests of about 400 X₁ males. Meiosis was examined in X₁ males which showed conspicuous chromosomal rearrangements in their somatic cells. The absence of either heteromorphic chromosome pairs or multivalents at spermatogenesis and the failure of the X₁ males to transmit any form of chromosome aberration induced by paternal irradiation is strong evidence that the heterochromatic chromosomes are destroyed in P. oleae. — The evolutionary relationships of the chromosome systems in the coccids are considered. Models are outlined for the derivation of a Comstockiella system involving chromosome destruction either from a lecanoid sequence or from a hypothetical Comstockiella sequence involving chromosome pairing. Problems concerning the control of chromosome destruction are discussed.From a dissertation submitted in partial fulfillment of the requirements of Doctor of Philosophy in Genetics.This work was supported by grant GB 8196 from the National Science Foundation to Dr. Spencer W. Brown, and by a National Institutes of Health Fellowship 1 F02 CA 44173-01 to the author from the National Cancer Institute.Dedicated to Dr. Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

Destruction of specific heterochromatic chromosomes during spermatogenesis in the Comstockiella chromosome system (Coccoidea: Homoptera)

In male coccids with the Comstockiella chromosome system, the set of chromosomes of paternal orgin becomes heterochromatic (H) during early cleavage. Just prior to prophase I of spermatogenesis, some of the H chromosomes are destroyed; the rest are eliminated following meiosis. In this report a Comstockiella sequence is described from Dactylopius opuntiae (2n=10) in which one chromosome pair is about three times longer than the others. During prophase I the number of small H chromosomes present varied from cyst to cyst, but the long H chromosome was present in every cyst. These observations provide the best evidence to date that in the Comstockiella system a particular chromosome may always escape destruction. An analysis of Kitchin's (1975) data about the frequency of prophase I cysts with 1–4 H chromosomes in three species of Parlatoria with 2n = 8 suggested that in these species chromosomes of similar size may have very different probabilities of being destroyed. Evidence that in other species with the Comstockiella system a particular H chromosome is always retained is reviewed, and the possibility that in Ancepaspis tridentata the variation in the length of the H chromosome retained is due to the partial destruction of the longest chromosome is discussed.     

The Comstockiella system of chromosome behavior in the armored scale insects (Coccoïdea: Diaspididae)

Summary The Comstockiella chromosome system occurs in the armored scale insects and the closely allied palm scales. During development of the males, the paternal chromosome set becomes heterochromatic and remains so until spermatogenesis. With the exception of one chromosome, the heterochromatic complement loses its differential aspect during early spermatogenesis and its members pair with their euchromatic homologues There is but one division during which the two components of each bivalent separate to opposite poles. Both division products form sperm.One pair of chromosomes, the D pair, always shows differential behavior. The D pair usually does not form a bivalent. The heterochromatic homologue, D^H, divides equationally and is eliminated by anaphase lagging or telophase ejection; its daughter halves remain as pycnotic residues during the early phases of spermiogenesis. The euchromatic homologue, D^E, also divides equationally to contribute to both of the telophase nuclei. Compensation for the division of the D^E univalent may occur during either the early or late phases of spermatogenesis.In some species the D pair is a fixed entity, analogous to the sex chromosomes in this regard. In other species, more than one pair may be elected to the D role, but only one at a time, and always the same one within each cyst.Taxonomic evidence indicates the Comstockiella system was derived from the lecanoid system, previously known from the work of the Schraders and others. In the lecanoid system, the paternally derived heterochromatic set divides equationally, along with the euchromatic set, during the first spermatogenic division. During the second spermatogenic division, the two sets are segregated from each other. The two euchromatic derivatives form sperm while the heterochromatic derivatives persist for a while as pycnotic residues. Both the lecanoid and Comstockiella systems occur in some species often in the same testis, but only one of the two systems within any one cyst.The discussion is devoted to an analysis of the mode of inheritance expected in the Comstockiella system and its evolutionary derivation. The Comstockiella system may have been derived in a step-by-step fashion from the lecanoid. The two systems differ by four processes which occur at spermatogenesis in the Comstockiella but not the lecanoid system; these are (1) deheterochromatization, (2) chromosome pairing, (3) compensation for the extra division of the D^E chromosome, and (4) lagging or ejection to eliminate the D^H chromosome.In addition, the residual genetic effects of the heterochromatic set may have undergone considerable change before the lecanoid system could evolve into a Comstockiella. Once the evolutionary step were otherwise possible, mechanistic features would aid and abet the emergence of the new system even though it lacked immediate selective advantage.The variable-D aspect of some examples of the Comstockiella system cannot be readily understood in terms of known examples of chromosome behavior; an admittedly highly speculative hypothesis is offered in an attempt to explain the situation.The diaspidid system, in which the paternal chromosomes are eliminated at late cleavage, is believed on taxonomic grounds to have stemmed from the Comstockiella, and forms the final stage of the four-step evolutionary sequence. Necessary changes for the derivation of the diaspidid system from the Comstockiella are discussed.This work was begun during the tenure of a Guggenheim Memorial Fellowship, 1956–57, and has subsequently been supported in part by grants from the National Science Foundation (G-4497 and G-9772).     

Chromatin organization in the male germ line of Drosophila hydei

The chromatin organization in developing germ cells of Drosophila hydei males was studied with the highly sensitive DNA stain DAPI (4, 6-diamidino-2-phenylindole dichloride). The prophase of meiosis I is characterized by decondensed chromosomes and only late during this stage do they condense rapidly. The sex chromosomes show allocycly. During postmeiotic development the final condensation of chromatin is preceded by a cycle of condensation and subsequent decondensation. Meiotic chromosomes were studied in more detail after orcein staining. Pairing sites of the sex chromosomes could be localized in the distal end of the heterochromatic arm of the X chromosome and distally in both arms of the Y chromosome. The various heterochromatic parts of the genome condense differentially in meiosis. Chromatin reorganization was studied cytochemically with antibodies raised against histones H1 and H2A of D. melanogaster. The core histone H2A is present in spermatid nuclei until the late elongation stage. However, histone H1 is not found in the chromatin later than the early primary spermatocyte stage. Thus, chromatin reorganization during spermatogenesis in D. hydei is complex. The process is discussed with regard to possible functions.     

Nonreplication of heterochromatic chromosomes in a mealy bug,Planococcus citri (Coccoidea: Homoptera)

In males of mealy bugs with the lecanoid chromosome system, the paternal set of chromosomes becomes heterochromatic in early embryogeny. In males of the mealy bug, Planococcus citri, the heterochromatic (H) set in testis sheath cells and in most of the oenocytes apparently did not replicate while the euchromatic (E) set was undergoing several cycles of endoreplication. In third instar males, testis sheath cells in endoanaphase and endotelophase exhibited 5H and either 40 or 80E chromosomes. The increase in the number of E chromosomes was attributed to the replication of only the E chromosomes. Oenocytes of third instar males had 0, 5, or 10H chromosomes and from 10 to 240E chromosomes. The oenocytes with 5H chromosomes had a mean of 50.8E chromosomes, and those with 10H chromosomes had a mean of 155.6E chromosomes. Nuclear and cell fusion was considered as a means of producing the various numbers of H and E chromosomes in oenocytes, and it was concluded that although nuclear fusion probably took place, the differences between the number of H and E chromosomes was at least in part due to replication of only the E chromosomes. The size of the H chromosomes was about the same in all the testis sheath cells and the oenocytes irrespective of the level of endopolyploidy for the E set. These H chromosomes apparently did not increase in polyteny, because they were only about half the size of the H chromosomes in prophase I of spermatogenesis. The significance of the nonreplication of the H set and the control of nonreplication are briefly discussed.This study was aided by a grant (GB-1585) from the National Science Foundation, Washington, D.C.     

Chromosome systems in the eriococcidae (Coccoidea Homoptera)

Spermatogenesis is described in two eriococcid species and the observations are compared to those previously reported. In Gossyparia spuria the diploid chromosome number is 28 in both males and females. In the female all the chromosomes are euchromatic. In most male tissues 14 of the chromosomes are euchromatic (E) and 14 are heterochromatic (H). Prior to the first meiotic division in males the number of H chromosomes was reduced. During prophase I all the cells showed 14 E chromosomes and from 1 to over 9 H chromosomes. The range of chromosome numbers in metaphase I was similar to that in prophase I. All the chromosomes divided in anaphase I, and, following differential uncoiling at interkinesis, the E and H groups of chromosomes segregated from each other at anaphase II. Only the E groups formed sperm. The presence of a variable number of H chromosomes and a haploid number of E chromosomes in spermatogenesis suggested the presence of the multiple-D variant of the Comstockiella chromosome system. In this system some of the H chromosomes become euchromatic prior to prophase I of spermatogenesis and pair with their E homologues. All the remaining H chromosomes are thus univalents, while among the E elements, some are univalents and the rest are bivalents. The observed reduction in the number of H chromosomes in the first meiotic division which was previously attributed to pairing among the H chromosomes, is now interpreted to be the result of the return of some of the H chromosomes to a euchromatic state and to their subsequent pairing with their E homologues. Spermatogenesis in Eriococcus araucariae was similar to that of G. spuria except that the reduction in the number of H chromosomes was not as extensive. The chromosome systems of the two species are compared to those of other eriococcids and the differences are briefly discussed.Supported by grant GB1585 from the National Science Foundation, Washington, D. C.     

Intranuclear destruction of heterochromatin in two species of armored scale insects

Spermatogenesis is described in two species of armored scale insects,Parlatoria proteus andParlatoria ziziphus. In the males of both species, a haploid set of four chromosomes becomes heterochromatic during early embryogeny. The heterochromatic chromosomes are lost later by two different mechanisms during spermatogenesis. Just before meiosis begins one or more heterochromatic chromosomes disappear from each primary spermatocyte as a consequence of a rapid intranuclear chromosome destruction. Meiosis consists of a single achiasmatic division. At prophase four euchromatic and from one to three heterochromatic chromosomes are present in each cell. Although both the euchromatic and remaining heterochromatic chromosomes divide, the heterochromatic chromosomes are later eliminated by posttelophase ejection; the eliminated chromosomes then disintegrate slowly in the cytoplasm. Each of the two species displays a species specific level of heterochromatin retention and both differ in this regard from the previously describedParlatoria oleae. The evolution of a chromosome system involving intranuclear chromosome destruction is discussed.     

Localized euchromatinization of the X chromosome during spermatogenesis in the grasshopper Melanoplus femur-rubrum

In grasshoppers, as well as in most other animals, the X chromosome is heteropycnotic (heterochromatic) during prophase I and metaphase I of spermatogenesis. During the same stages, in some of the cells of three Melanoplus femur-rubrum males (out of several hundred males examined) part of the X appeared euchromatic (E). In one male, the E segment was observed in 90% of the cells of a single cyst in which all the cells lacked one of the smallest autosomes. In another cyst of the same follicle all the cells contained one additional small autosome, and none of the Xs exhibited an E segment. The size of the E segment suggested that it resulted from the failure of part of the X to become heteropycnotic prior to the formation of the cyst. In the other two males, many of the cells contained chromosome fragments and translocations. In many cells in which the X exhibited an E segment, however, there was no evidence of chromosome breakage. The E segments were sometimes terminal and sometimes interstitial in the same cyst. This variation suggested that they resulted from the euchromatinization of part of the X immediately prior to prophase I of meiosis. Because fragmentation and the presence of Xs with an E segment were each very rare, it was concluded that they were in some way causally related. It was also concluded that in this species the heterochromatinization of the X is not controlled by a single inactivation center.     

Asymmetrically heteropycnotic X chromosomes in the grasshopper Melanoplus femur-rubrum

In short-horned grasshoppers the X chromosome is negatively heteropycnotic in at least some of the spermatogonia but is positively heteropycnotic (heterochromatic) during prophase I of spermatogenesis. In tetraploid (4n) spermatocytes in prophase I the two Xs present have so far been reported always to be heterochromatic and unpaired. In several males of the grasshopper Melanoplus femur-rubrum (Acrididae), however, some of the 4n primary spermatocytes contained one heterochromatic X (X_h) and one euchromatic X (X_e). This asymmetry of heteropycnosis (AH) was first observed in grasshoppers by M.J.D. White who observed it, however, only in 4n spermatogonia in which one X was negatively heteropycnotic and the other was isopycnotic (euchromatic). In M. femur-rubrum the AH involved both positive and negative heteropycnosis. In some of the 4n cells both Xs were heterochromatic and these cells were usually present in small groups but sometimes comprised whole cysts. The 4n cells with X_e+X_h always comprised several whole cysts in a follicle or whole follicles. The origin of the two cell types may be explained by assuming that heteropycnosis originated prior to the origin of the cysts, that when, as a result of polyploidization, two Xs were present in a 4n cell only one became heteropycnotic, and that the state of the X (X_h vs. X_e) usually persisted into meiosis. The 4n primary spermatocytes exhibiting AH divided regularly during the first meiotic division but following telophase I they usually failed to undergo cytokinesis and to enter the second meiotic division. The available evidence suggests that the arrest of these cells is the result of the genetic activity of the X_e in those stages in which the X is usually heterochromatic and genetically inactive. The relationship between AH and facultative heterochromatinization is discussed and it is concluded that the present observations put into question the validity of previous models attempting to explain facultative heterochromatinization (including that of the X in the mammalian female).     

The pattern of DNA replication in the chromosomes of Puschkinia libanotica

The uptake of H³-thymidine into the chromosomes of Puschkinia libanotica has been studied in plants possessing or lacking a heterochromatic B chromosome. The pattern of H³-thymidine uptake by the A chromosomes at the end of the S phase is similar in plants of both genotypes. Regions around the centromere take up more H³-thymidine at the end of S than do more distal regions. The rate of uptake into the heterochromatin of the B chromosome increases towards the end of S, but there is no evidence that synthesis in the B chromosome carries on after the completion of DNA synthesis in the euchromatic A complement. It is proposed that at the end of the S phase more replicons in the heterochromatin of the B chromosome are engaged in DNA synthesis than in euchromatin.     

Phyletic and evolutionary relationships ofBrachyscome lineariloba (Compositae)

A comparison of karyotypes ofBrachyscome breviscapis (2n = 8),B. lineariloba cytodemes E (2n = 10), B (2n = 12) and C (2n = 16) suggests that these species have a homoelogous basic set of four chromosome pairs, two large pairs and two small, and that theB. lineariloba cytodemes E, B and C are related toB. breviscapis by successive additions of small chromosomes. A pronounced asynchrony of chromosome condensation between these large and small chromosomes has been observed. In the artificial hybrids betweenB. dichromosomatica (2n = 4) ×B. breviscapis, and theB. lineariloba cytodemes, theB. dichromosomatica chromosomes are similar in size and condensation behaviour to the small chromosomes ofB. breviscapis and ofB. lineariloba cytodemes E, B and C. Meiotic pairing in these hybrids also demonstrates the strong affinities between these chromosomes. It is suggested thatB. breviscapis may be of amphidiploid origin between a species with two large early condensing chromosome pairs and another,B. dichromosomatica-like species with two small late condensing pairs. It seems most likely that the additional small and late condensing chromosomes inB. lineariloba cytodemes E, B and C are derived from theB. dichromosomatica-like parent, and that each addition increases vigour, fecundity and drought tolerance, allowing these cytodemes to colonize more open and arid environments. Transmission of the univalents in the quasidiploidB. lineariloba cytodeme E was verified as being via the pollen, and not via the embryo sacs.The cytology ofBrachyscome lineariloba (Compositae, Asteroidae), 10.     

The chromosomes of Puschkinia libanotica during mitosis

The chromosome complement of Puschkinia libanotica is described. In addition to five pairs of A chromosomes plants may possess up to 7 B chromosomes. Part of the long arm of the B chromosome gives rise to a heterochromatic mass in interphase nuclei and this can be seen to be a double structure in G₁ nuclei and a quadruple structure in G₂ nuclei. It is believed that these configurations represent the pre- and post-replication forms of subchromatids in the heterochromatic segment of the B chromosome. Microdensitometry of metaphase chromosomes shows that the segment of the B chromosome that is heterochromatic during interphase has no more DNA per unit volume than any of the euchromatic A chromosomes.     

The ecology of the calanoid copepod Eurytemora affinis in salt marsh tide pools

We describe selected aspects of the ecology of the copepod Eurytemora affinis in tide pools of an inland salt marsh near L'Isle-Verte, Québec along the southern shore of the St. Lawrence estuary. E. affinis performed daily horizontal migrations moving from the centers of pools to the banks and into dense algae. Male E. affinis were mainly found in the center of the pools during twilight (21 : 00 hrs) and in dense algae in daylight (12: 00 hrs) whereas most females and copepodites were found near the banks at all three sampling periods. Although these daily movements among sites may have minimized predation by diurnally foraging sticklebacks (Pisces: Gasterosteidae), other explanations for the movements can not be excluded. We also quantified the effects of fish predation upon the population structure of E. affinis. Densities of all stages (nauplius, copepodite, adult) were significantly lower in pools with fish than in pools without fish. Female E. affinis were significantly smaller (mean length) in pools with fish than in pools without fish, indicating that the sticklebacks selectively ate larger females. Male-biased sex ratios were found in both types of pools, which excluded the possibility that biased ratios in this species are caused by selective predation upon the females.     

Cytogenetics of two species of Euceraphis (Homoptera,Aphididae)

Somatic cell divisions, spermatogenesis, and the prophase stages of primary oocytes, are described for two species of birch aphid, Euceraphis betulae (Koch) and E. punctipennis (Zetterstedt). Females of E. betulae have two autosome pairs, two pairs of X-chromosomes of different lengths, and two B-chromosomes. Females of E. punctipennis have the same number of X-chromosomes and B-chromosomes as E. betulae, but only a single pair of autosomes. The sex determination system is X₁X₂0. E. punctipennis males sometimes have only one B-chromosome. In the spermatogenesis of E. betulae, pairing of homologous autosomes occurs in early prophase I, but no evidence was found of chiasmata or end-to-end alignment of homologues. Instead, homologues remain closely aligned in parallel as they condense into metaphase, and anaphase I separates the products of pairing in a strictly reductional manner. The two unpaired X-chromosomes and both B-chromosomes are stretched on the anaphase I spindle and all four pass into the larger secondary spermatocyte. The second division is equational. The B-chromosomes thus show accumulation in spermatogenesis, which must be compensated in some way by an elimination mechanism in oogenesis. Meiosis of E. punctipennis is highly anomalous. The two autosomes pair but separate again in early prophase I, then one homologue becomes heterochromatic and is apparently rejected from the late prophase nucleus. A single, equational maturation division follows. In female meiosis I, both species show highly characteristic diplotene figures with multiple chiasmata, the B-chromosomes remaining unpaired. These results are discussed in relation to previous work on aphid cytogenetics.     

A supernumerary chromosome with an accumulation mechanism in the lecanoid genetic system

Summary The supernumerary chromosomes of a mealy bug,Pseudococcus obscurus Essig are heterochromatic but show a variable heteropycnosis. In the female, they are weakly heteropyonotic in most tissues, but in a few tissues the individual supernumeraries form striking chromocenters. At oogenesis, they remain unassociated and divide equationally during the first division; during the second, they pair and disjoin. Pairing is usually accomplished by twos so that an unpaired supernumerary is found whenever an odd number, or only one, is present; the unpaired entity is twice as likely to go to the second polar body as to the egg.The normal spermatogenesis in the mealy bugs is a highly modified meiosis in which the paternal heterochromatic set is eliminated from the genetic continuum; during this sequence the supernumeraries are fully heterochromatic up until late prophase I. They then undergo a sharp change in pycnosis and become negatively heteropycnotic. In the second meiotic division they usually segregate with the maternal euchromatic set. Their behavior during spermatogenesis thus becomes an accumulation mechanism since an unreduced number, or nearly that, is transmitted by the males.The variable behavior of the supernumeraries affords further insight into the problem of heterochromatization in the mealy bugs.The supernumeraries may have originated from fragments followed by subsequent duplications. The accumulation mechanism may have been an important factor in their establishment.In genetic systems in which the supernumeraries have an accumulation mechanism, an elimination mechanism might evolve to stabilize the number of supernumeraries. Such elimination mechanisms are known for other genetic systems but have not yet been developed in this mealy bug.The material in this paper is part of a dissertation submitted to the graduate school of the University of California in partial satisfaction of the requirements for the degree of Doctor of Philosophy. This work was supported in part by a National Science Foundation Grant (G-9772) to ProfessorSpencer W. Brown.Predoctoral Trainee in Genetics, National Institutes of Health, 1960–1961.     

Accumulation of B-chromosomes by preferential segregation in females of the grasshopper Melanoplus femur-rubrum

In a population of Melanoplus femur-rubrum 13.9% of the males and 9.1% of the females sampled possessed a metacentric B chromosome (B). In crosses of females with one B (1 B females) and 0 B males 0.82 ± 0.05 of the offspring received the B. The value expected from Mendelian segregation is 0.5. In crosses of 1 B males and 0 B females the frequency of offspring receiving the B was 0.53 ± 0.02. The B is heterochromatic during prophase I of spermatogenesis but is euchromatic during prophase I of oogenesis. The observation that in 1 B females only one B was present in metaphase I of oogenesis suggested strongly that the high rate of transmission of the B by the females resulted from preferential segregation of the B into the secondary oocyte. The maintenance of the B in the species in discussed.Supported by Grant GB 23665 from the National Science Foundation, Washington, D.C.     

Nucleotide variation and molecular structure of the heterochromatic repetitive AluI DNA in the brine shrimp Artemia franciscana

Summary It has been suggested that DNA bending could play a role in the regulation of gene expression, chromosome segregation, specific recombination and/or DNA packaging. We have previously demonstrated that an Alul DNA family of repeats is the major component of constitutive heterochromatin in the brine shrimp A. franciscana. By the analysis of cloned oligomeric (monomer to hexamer) heterochromatic fragments we verified that the repetitive AluI DNA shows a stable curvature that determines a solenoidal geometry to the double helix. This particular structure could be of relevant importance in conferring the characteristic heterochromatic condensation. In this paper we evaluate how the point mutations that occurred during the evolution of the Alul sequence of A. franciscana could influence the sequence-dependent tridimensional conformation. The obtained data underline that, in spite of the high sequence mutation frequency (10%) of the repetitive DNA, the general structure of the heterochromatic DNA is not greatly influenced, but rather there is a substantial variation of the copy number of the repetitive AluI fragment. This variation could be responsible for the hypothetical function of the constitutive heterochromatin.Offprint requests to: N. Landsberger     

Indagini e Osservazioni Sui Danni Provocati Dalle Minime Termiche del Febbraio 1956 Agli Olivi Nei Vivai di Pescia (Toscana)

Abstract

Cytotaxonomic notes on the genus Biarum Schott (Araceae) in Italy. Morphological and caryological observations on sicilian and italian specimens of Biarum tenuifolium (L.) Schott could not prove its taxonomic separability from B. cupanianum Paglia. In our opinion the latter is to be considered as a synonym of the former. The chromosome number of B. tenuifolium is very variable (2n = 16, 20, 26); the chromosomes show eu- and heterochromatic regions. A sardinian plant usually assigned to Biarum bovei Blume needs further studies in order to verify its taxonomic identity.     

Chromosome systems of the Eriococcidae (Coccoidea-Homoptera)

A survey of chromosome systems in the Eriococcidae shows that many of them are intermediates between two systems occurring elsewhere in the coccids. These two systems differ in the number of paternal chromosomes which remain heterochromatic during spermatogenesis and are then discarded. In the lecanoid system, all are discarded; in the Comstockiella system only one, the D^H chromosome is discarded. Evolutionary steps from the lecanoid to the Comstockiella systems had previously been postulated with the intermediates having from n-1 down to 2 chromosomes remaining heterochromatic during spermatogenesis. The transition was believed to be reversible and the systems therefore inherently unstable. Most of the armored scales with Comstockiella systems have not shown intermediacy but one case has been recently reported. The eriococcids as a family are characteristically intermediate with frequently extreme variation from cyst to cyst in number of chromosomes remaining heterochromatic. Species with an unmodified Comstockiella system may occur but are in a minority. One unanticipated system is reported for two species, the complete Comstockiella system in which all the heterochromatic chromosomes are reversed at spermatogenesis; this system is also theoretically unstable. Indirect evidence for the great antiquity of the eriococcids is presented, and the question raised as to the maintenance of instability over several epochs. Comparative cytology may provide part of the answer to this question. The most common, and probably the basic diploid chromosome number of the eriococcids is 18, with a range from 12 to 28 and about 48; decreases in number are more frequent than increases.This work was part of a research program on coccids supported by grants from the National Science Foundation currently GB 4289.