282 PKOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Avere 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 wliicli 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 snout in the female as compared with the 

 slender, either elongated or short, and pointed snout of specimens with 

 the lobulated organs. 



"2. A ligliter coloration of the female, usually quite green on the back 

 and yellowish or yellow on the bellj', 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 usuallj^ whitish on the belly. 



" 3. A further and important external character is an api^reciable differ- 

 ence in the height of the dorsal fin (a point confirmed by me). All 

 the females have a distinctly higher and wider dorsal than males of the 

 same size. 



"4. And, finally, we may note, although not a constantly a])preciable 

 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 

 females are equally common." 



Jacoby then gives some measurements, the averages of a great num- 

 ber of eels measured by him, from which the actual value 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 Fisclifang iu der Lagune voa Cominacluo. 



