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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 DH 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.

1. Chromosome behavior at spermatogenesis has been described for one species each of three families of coccids not previously studied in this regard: Cerococcus quercusComstock of the Asterolecaniidae, Conchaspis lepageiHempel of the Conchaspidae, and Tachardiella sp. of the Lacciferidae. All three families belong to Balachowsky's “lecanoid” section of the coccid superfamily, and the first two have been suggested, by various systematists, as close allies of the armored scales (Diaspididae). 2. All three species showed lecanoid chromosome behavior, as originally described by the Sohraders, in that one haploid set of chromosomes is heterochromatic in the males and eliminated at spermatogenesis. The exceedingly clear cytology of C. quercus permitted a detailed study of the critical second division stages when the euchromatic and heterochromatic sets are separated. Although considerably more difficult cytologically, both the other species showed a typical lecanoid pattern of behavior; in addition, both showed an accessory structure, of unknown origin and function, which was present during the meiotic sequence. 3. The cytological and taxonomic implications of the results are considered, largely on a comparative basis, in the discussion. Special attention is given to the problem of the origin of the armored scales and also to Buchner's recent suggestion of the possible influence of symbionts on sex determination.

Cytologically, Puto has proved more primitive than its taxonomic position would indicate. In the single previously described example (Hughes-Schrader, 1944), an uncomplicated inverted meiotic sequence was described for the males. The present example, P. albicans, showed a significantly more primitive inverted sequence. Unlike the other examples reported for aphids and coccids, the chromatids of the dyads neither dissociated nor reassociated during interkinesis. Instead, they remained closely associated and interconnected by an unresolved terminal chiasmate attachment. At first metaphase, the spindle attachments were localized to a restricted region of the poleward surface of the chromatids. Localization of attachment during meiosis and close association of chromatids during interkinesis are both suggestive of similar but not identical conditions expected in ancestors with an uninverted meiotic sequence. A second species proved intermediate between P. albicans and that described by Hughes-Schrader in which a complete cycle of dissociation and reassociation occurred during interkinesis. In P. albicans the pachytene bivalents showed no structures suggestive of centric localizations. At their greatest condensation at first metaphase, the chromatids were clearly subdivided into half chromatids. Limited observations were made on chromosomes of other species of Puto and of Phenacoleachia zealandica, and also on spermiogenesis and mycetocyte formation in Puto. The discussion is devoted to considerations of chromatid subdivision, holokinetic chromosomes, and meiotic inversion and some evolutionary implications are mentioned.

Conventional types of cytogenetic studies with the mealybug, Planococcus citri (Risso), are possible with the use of genetic markers and meiotic analysis in the female. The loci of an eye-color mutant, salmon, and a wing-shape mutant, banjo, are linked with about 22 per cent recombination. These markers have been used in the identification and maintenance of lethals and rearrangements. All the cytologically identifiable rearrangements have proved to be reciprocal translocations, some symmetric, others, grossly asymmetric or otherwise complicated. No simple breakage products have been recovered. On the basis of their effects on crossing over, some of the lethals are believed to be associated with small rearrangements. The bivalents normally have one chiasma; only 1.2 per cent have two. Interference is decidedly decreased in chiasma formation in translocation heterozygotes, and in genetic recombination with suspected small rearrangements associated with lethals; it is also decreased, but less markedly, in genetic recombination with lethals in translocations. These various results are discussed in relationship to the holokinetic nature of the coccid chromosome, and natural increases in coccid chromosome number, as well as in regard to the effect of rearrangements on interference.