"All such beliefs as have been thus recounted are due to the inconspicuous nature of the generative organs in eels found in fresh waters and at most seasons—a characteristic which is in strong contrast to the development of corresponding parts in fishes generally. Nevertheless the ovaries of the eel were discovered, as long ago as 1707, by Dr. Sancassini of Comacchio, and described by the celebrated Valisneri (after whom the plant _Valisneria_ was named) in 1710, again by Mondini in 1777, and almost contemporaneously by O. J. Müller of Denmark. Later the illustrious Rathke (in 1824, 1838, and 1850) and also Hornbaum-Hornschuch published the results of special investigations, and figured the eggs. But it was only in 1873 (after several futile endeavors by others) that the male organ of the eel was recognized, also by an Italian naturalist, Dr. Syrski, in small individuals of the species, and a previous idea that the eel was hermaphroditic thereby dispelled. The sexual differences are correlated with external ones, and generally the males and females, when adult, can be told apart. Jacoby testifies that he examined large numbers with a view to solve this question. The most important differences relate to (1) size; (2) form of the snout; (3) color; (4) dorsal fin; and (5) size of the eyes. (1) The males rarely attain a length of more than seventeen to nineteen inches, while adult females are generally much larger; (2) the snout in the male is attenuated and rather pointed, while in the female it is comparatively broad and blunt; (3) the male is of a deep darkish green, or often a deep black with a shining luster and a whitish belly, while the female has a clearer color, usually of a greenish hue on the back and yellowish on the belly; (4) the dorsal fin is lower and less developed in the male than in the female; and (5) the eye of the male is large and that of the female, as a rule, comparatively small. These characters, however, do not always hold good. Jacoby remarked that 'special reference having been paid to the height and narrowness of the dorsal fin, much success has been met with in picking out, in the fish-market of Trieste, the eels which possessed the organ of Syrski (that is, the male organ); absolute certainty, however, in recognizing them cannot be guaranteed. If one is searching among living eels with no characters in mind,—with the exception of the first, that of length,—he will find in every ten eels, on an average, eight females and two with the supposed male organ; but if the selection is made with a careful reference to all these marks of difference, the proportion changes, and out of every ten examples about eight will be found with the supposed male organ.'