Abstract
This dissertation comprises the results of five microscopical studies addressing issues related to sexual reproduction. The main focus of the first two studies (Chapters 1-2) on water snail hybrids lies on chromosomal differences and their potential involvement in isolation mechanisms between these hybridizing species. The two studies on the yellow dung fly Scathophaga stercoraria were aimed at investigating either anatomical structures (Chapter 3) or physiological processes (Chapter 4) involved in sperm transport and utilization with special reference to the potential of female control of these processes. The Chapter 5 consists of supporting material on the karyotype of Scathophaga stercoraria.
Sbilordo, S