282 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 
were made with a Zeiss immersion, objective K, oculars 2 and 3. 
According to Jacoby,* Von Seibold saw similar strings of cells in an 
eel, in which the lobes were very strongly developed. These strings of 
cells presented to the eye the most undoubted similarity to the testicular 
mother cells of spermatozoa. I also believe that the strings of cells ob- 
served by me must be regarded as such. In no case did I observe any 
spermatozoa. 
Previous to my investigations into the histology of the testicular 
lobes of the eel, I occupied myself with the question whether there were 
not some other external characters distinguishing the sexes besides the 
already mentioned difference in size and length. Jacoby remarks as 
follows upon this point: 
“1, A distinctly broader sneut in the female as compared with the 
slender, either elongated or short, and pointed snout of specimens with 
the lobulated organs. 
“2. A lighter coloration of the female, usually quite green on the back 
and yellowish or yellow on the belly, whilst the other sex is much darker 
green in color, often an intense black on the back, with always a more 
marked metallic luster on the sides, and usually whitish on the belly. 
“5. A further and important external character is an appreciable differ- 
ence in the height of the dorsal fin (a point confirmed by me). All 
the females Lave a distinctly higher and wider dorsal than males of the 
same size. 
“4, And, finally, we may note, although not a constantly appreciable 
character, the greater diameter of the eye of the male. Eels with strik- 
ingly small eyes seem almost always to be females. Eels which have a 
Syrskian organ usually have relatively large eyes, though large-eyed 
femalés are equally common.” 
Jacoby then gives some measurements, the averages of a great num- 
ber of eels measured by him, from which the actual vaiue of his charac- 
ters becomes apparent. I believe, nevertheless, that he attaches too 
much importance to some of his characters, and some others, not less 
important, he has not noticed at all. 
Out of a great number of eels measured by me I select the following, 
in which the measurements given in the parallel rows are taken from 
pairs the lengths of which are, as nearly as possible, the same: 
“Dr. L. Jacoby, Der Fischfang in der Lagune von Commachio. 
