In the scope of a genetic control research project gametogenesis of the onion fly, Hylemya antiqua
(Meigen), is studied as a base for investigations on radiation histopathology of the gonads.
Various cytological, histological, electronmicroscopical and autoradiographical methods, including investigation of living male germinal cells, are used.
The gross anatomy of the male and female reproductive systems is simple as compared to other insect species.
In newly hatched larvae the gonads contain on an average 13 germinal cells. Gonads in larvae which are less than 7 days old cannot be distinguished as being male or female. This distinction becomes possible after the apical cell and the apical somatic tissue respectively is formed in the young gonad.
Spermatogenesis is treated in a number of paragraphs dealing with the description and identification of germinal and somatic cell types, the ontogenetic development of the testis, the dynamics of spermatogenesis and aspects of comparative spermatogenesis.
A proper identification of the testicular cell types is considered to be imperative to any correct experimental approach of spermatogenesis. Morphological descriptions of the various germinal and somatic cell types are given accordingly. New elements are the observation of spermatogonial cells which show in their nucleus a varying degree of chromatin concentration. A similar phenomenon is observed in somatic cell types. Testicular cavities namely the apical cavities and the central cavity are described as are the somatic central cavity cells and the basal cells in the testis.
The ontogenetic development shows the structure and function of the testis during the larval, pupal and adult stages of the life cycle. At the end of the larval stage differentiation of primary spermatogonia starts, leading to sperm production which takes place in the late pupa and the young adult. During adulthood the testis function changes from sperm production towards sperm storage.
Based on counts of the number of cells per cyst of germinal cells it is supposed that various systems of spermatogonial multiplication operate in these populations. Primary spermatogonia may be denoted as being 'predefinitive' which indicates their presumed role in the multiplication processes. The number of definitive spermatogonial divisions may vary according to the acting multiplication system. The speed of formation of different spermatogenic cell types is revealed by incorporation of 3 H-thymidine in the spermatogonia. Development of a primary spermatogonium into sperm cells lasts about 10 days.
Comparison of mainly morphological features of male germinal cell types in a number of insect species, including H. antiqua,
indicates possibilities for comparative research of spermatogenesis in various insect species. This could provide a basis for comparative radiobiological or other experimental investigations on insect spermatogenesis.
Female germinal cell types and somatic cell types of the ovary are described. The ontogenetic development of the ovary shows ovariole differentiation in the young pupal ovary. In late pupal ovaries egg chamber formation begins its iterative course which is continued during adulthood. Egg chamber formation has been divided into ten stages.
Spermatogenesis and oogenesis share a number of features, which suggests a certain similarity of the processes involved.