By Franz Engelmann and G. A. Kerkut (Auth.)

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Based admittedly on insufficient evidence, we may speculate on its presence in species other than Lampyris. For example, some males of the membracid Thelia bimaculata which were parasitized during an early instar may change their external morphology (size and color) to that of a female (Kornhauser, 1919). Neither parasitized females nor parasitized older male larvae changed. Can one assume that the parasite destroyed the apical mesodermal tissues of the testis follicle and that therefore no androgenic hormone was liberated?

14). 9 1965). In Rhyacionia buoliana mature spermatozoa are found shortly after pupation (Shen and Berryman, 1967). The same GONADAL DEVELOPMENT 43 FIG. 13. Schematic representation of the sequence of sperm differentiation. ) observations can be made for many additional species, but these quotations should suffice to illustrate the point. Quite in contrast to this, in species with a long adult life span, the full process of spermatogenesis may take place after emergence. Both brooding procedures and labeling techniques gave convincing evidence for this.

In support of this hypothesis, we may cite the thelytokous Ooencyrtus submetallicus which produces functionless males if reared at 29°C or above (Wilson and Woolcock, 1960); the cytogenetic mechanism for thelytoky seems to break down at elevated temperatures. It is noteworthy that closely related species are exclusively arrhenotokous (Wilson, 1962). Parthenogenetic species have a certain advantage over bisexual ones in that their reproductive capacity is theoretically doubled. If a parthenogenetic strain arises within a population and these females are as fecund as those of the bisexual strain, the entire population may become parthenogenetic in time (Stalker, 1956).

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