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Part III. — Thirteenth Annual Report 



ovary has no oviduct. The genital pore opens externally into the urinary 

 aperture : internally it communicates with the Ussura recto-vesicalis 

 (frv.), a slit between the rectum (Rt.) and the urinary bladder (bl.) This 

 fissure joins the right and left portions of the abdominal cavity. Syrski 

 says : ' It is generally admitted that the eggs when loosened from the 

 ' ovaries fall indiscriminately into the abdominal cavity, but it is not said 

 1 which way they take in order to go out through the genital orifice. As 

 ' I have invariably found that the fully developed ovaries lean with their 

 ' outer surface against the side of the abdominal cavity, and approach 

 1 with their free edges the lower portion of the side, forming so to speak 



* a furrow, I must conclude that the loosened eggs descend between the 

 1 abdominal partition and the folds and leaflets of the ovary in the above- 

 1 mentioned furrow, and from it pass to the genital aperture without 

 ' scattering in the abdominal cavity. It is another of Rathke's erroneous 

 1 assertions, likewise maintained by others, that the genital opening through 

 ' which the eggs pass out from the abdominal cavity is formed by two 

 1 holes, a right one and a left. I have invariably found in all specimens 

 ' examined a simple aperture, which communicated with the right and left 

 ' halves of the abdominal cavity by means of a transverse fissure (fissura 

 1 recto-vesicalis) between the straight intestine and the urinary bladder and 

 1 opens into the urethra.' In the eels examined at St Andrews, one 

 genital aperture only was found. Internal to the ovary, and lying along 

 each side of the alimentary canal, there is usually a band of fat. ' * In the 

 ' ovary, which contains a great deal of fat, numberless eggs are imbedded. 

 ' By tearing a little piece of the ovary with a pin, and carefully wiping off 

 ' the small drops of fat, one can recognise the eggs with the naked eye 

 ' as very small white dots. The microscope will, however, distinctly 

 ' reveal their form and inner construction. They are generally round, 

 1 surrounded by a skin, which forms a clear transparent ring — the 

 1 zona yellucida. Inside of this skin there is a large mass of small 

 ' grains, the yolk of the egg. In the larger eggs nothing but these 



* grains is seen, especially when the eggs have lain in water for some time, 

 ' because then the small grains composing the yolk have congealed and 

 ' become opaque. But if one takes from the same ovarium the smaller 

 ' and less developed eggs, one may very distinctly recognise the small and 

 ' entirely colourless bladder, called the Purkinjean vesicle.' 1 f At any period 

 ' of the year, the ovary shows its ovules more or less developed, but like 

 ' those of all other osseous fishes, and its loose cellular tissue, which may 

 ' be reduced to a minimum towards the period of oviposition, or may, on 

 ' the contrary, subsequently become in part cellulo-adipose. The ovary 

 ' also always shows the narrow projections or thickenings of its surfaces 

 1 arranged parallel to each other. The folds run from the adherent to the 

 ' free margin, passing the latter in the form of small blunt denticulations. 

 ' Several authors, for example Valenciennes, say that in fresh water eels 

 ' are never seen with full milts, or full ovaries. This is only true for the 

 ' milt, or the contents of the testicle : but the ovaries are on the contrary 

 ' full of spherical ovules of a diameter of from T to 2 mm. during the 

 ' whole year. It is useless to insist here on the degrees of visibility of the 

 ' genninative vesicle, of the more or less granular nature of the contents of 

 1 the egg, or of the volume of the egg according to the season. During 

 ' summer the greater part of the eggs preserve the volume which they have 

 ' in winter, but they are less numerous than formerly, and the ground 

 ' tissue of the ovary includes adipose cells in greater or less numbers than 

 ' is seen at the time of the descent of the eels to the sea. In addition, 



* Jacoby, 'The Eel Question,' Report U.S. Fish. Comm., 1879. 



t Robin, 1 Les Anguilles males comparees aux femelles,' Journal de I' Anatomic 



et de la Physiologie, 1881, p. 437. 



