. - 138 — 



to Dr. ^ Petersen the young-fish trawl used on the "Thor", without which it would 



scarcely have been possible for me to procure within so short a time a picture of the 



distribution of the larvae of the eel over the almost looo miles distance from Iceland to 



the Bay of Biscay. 



Copenhagen, January ist, 1906 



Jolts. Schmidt 



SECTION I 

 Introduction 



Summary of the earlier investigations on the developmental history of the eel 



A. The older eels 



1. Male and female eels. In spite of the fact that extremely little is known 

 positively regarding the maturing and reproduction of the eel, there is perhaps no other 

 animal about which such a large amount has been written and just on these points. 

 Only a few of the many papers' which have been written on this subject from time to 

 time have however proved to be of lasting importance. In the following pages I shall 

 briefly mention the most important of the discoveries and observations, which may be 

 said to have advanced our knowledge on essential points towards the goal which will 

 sooner or later be attained, namely, complete knowledge of the biology of the eel 

 throughout its whole life. 



In the eels which usually come into the hands of investigators, the reproductive 

 organs are but little developed being far from mature. This tis he reason why we have 

 been comparatively speaking so late, much later than in the case of most of the other 

 common species, in arriving at definite knowledge regarding the presence and appearance 

 of the sexual organs in the eel. The Italian Mondini first described the ovary or female 

 genital organ of the eel in 1777, and the Dane 0. F. Müller independently in 1780. 

 The correctness of the determination was confirmed in 1838 by the German Rathke, 

 who later in 1850 further described a female eel, in the ovary of which he could detect 

 eggs 7io millimeter in diameter. Between Mondini's discovery in 1777 of the female 

 genital organs and the discovery of the male organs a period of a hundred years elapsed. 

 The reason for this may be found partly in the fact, that no one had noticed the pecul- 

 iarity that the male eels are considerably smaller than the females, and the males were 

 consequently being sought for amongst the large eels without result. In 1874 the Austrian 

 Syrski first described the male organ of the eel, and this has very often in consequence 

 been called "Syrski's organ", or on account of its fold-like appearance the "lobed organ". 



I See: JACOBY, Der Fischfang in der Lagune von Comacchio nebst einer Darstellung der Aalfrage. 

 Berlin, 1880. 



H. Chas. Williamson, On the reproduction of the eel (13th Annual Report of the Fishery Board for 

 Scotland for the year 1894, Part III. Edinburgh, 1895, p. 192). A very large selection of the literature is 

 given in these papers. In the present work therefore, only the works are cited which have been published 

 later than Jacoby's and Williamson's. 



