2 INTRODUCTION 



it develops a plainly visible urogenital papilla, the ovipositor, 

 with which it lays its eggs in freshwater mussels of the 

 genera Unto and Anodonta. Before and after spawning this 

 tube shrinks to a hardly visible nipple; but FleischMANN 

 and Kahn found that the ovipositor can develop at any time 

 into a long tube when estrogenic hormone is added to the 

 aquarium water. Struck by the similarity between this 

 phenomenon and the changes occurring in the mammalian 

 uterus during the rutting season, they concluded that the 

 estrogenic hormone in mammals must also be a physiological 

 estrogenic hormone in the fish. From our experiments, how- 

 ever, it has become clear that steroid mammalian hormones 

 affect the ovipositor indirectly, and that their influence on 

 the bitterling is probably pharmacological! 



We realized this when Bretschneider observed the 

 presence of numerous corpora lutea in the ovary of the 

 bitterling at the time of the growth of the ovipositor. He 

 further correlated the occurrence of these corpora lutea with 

 the presence of basophilic cells in the so-called gonadotrophic 

 zone of the anterior pituitary lobe. These basophils were 

 regarded as the restitution phase of the cells producing the 

 gonadotrophic hormone. After injection of an extract of the 

 hypophysis of the carp there was marked formation of 

 corpora lutea. When the hypophysis was removed, adminis- 

 tration of steroid hormones did not result in growth of the 

 ovipositor. Again, after ovariectomy, steroid hormones did 

 not cause growth of the ovipositor when the hypophysis was 

 left intact, whereas an extract from the ovary of Lophius 

 piscatorius containing corpora lutea caused appreciable growth 

 of the ovipositor in intact fishes. It seems, therefore, that the 

 steroid (mammalian) hormones influence the anterior pitui- 

 tary lobe (? via the hypothalamus), resulting in the secretion 

 of gonadotrophic hormone and the development of numer- 

 ous corpora lutea, whose hormone induces growth of the 

 ovipositor. 



Because of its ovipositor the female bitterling is well suited 

 to the investigation we had in view. Hence we subjected the 

 sexual-endocrine organization of this fish to an exhaustive 



