262 PROCEEDINGS OF THE ACADEMY OP [1884. 



PEELIMINARY OBSERVATIONS UPON THE BRAIN OF MENOPOMA. 

 BY HENRY F. OSBORN, SC. D. 



This is the second of a series of papers ^ upon the brains of 

 the American TJrodela. In tlie stud}^ of llenopoma, I have 

 detected numerous errors in the first paper upon Amphiuma,^ 

 and my attention has kindly been called to others by Prof. 

 Wilder and Dr. E. C. Spitzka. 



The brains of Amphiuma and Menopoma are even more alike 

 in their internal than in their external structure ; while the reverse 

 is the case in the comparison of Menopoma and 3Ienobranchus, 

 which resemble each other very closely externally, but in longi- 

 tudinal section present impoi'tant diflferences. 



The greater accuracy of the Menopoma work is due to changes 

 in technical methods. Before hardening, the brains were inflated 

 with Miiller's fluid, so as to preserve the natural proportion of 

 the cavities. After treatment with alcohol, they were placed for 

 a week in dilute carmine. Calberla's egg-mass was emploj'ed as 

 before, except that the A'-entricles were injected with the mass 

 before hardening. The delicate parts of the brain-roof were thus 

 retained. It appears now that celloidin may be used for this purpose 

 to equal, if not to greater, advantage in results, and with consid- 

 erable economy of time. The sections were cut in absolute 

 alcohol, were then floated upon a slide in consecutive order, from 

 twenty to fifty at a time, and were covered with a delicate slip of 

 blotting-paper during treatment with oil of cloves. These 

 changes greatly improved the three series, which were obtained 

 in as' many planes — horizontal, transverse and vertical to the long 

 axis of the brain. 



External Structure (PI. YI, figs. 1, 2, 3). 



With a single exception, and that an important one, the brain 

 of Menopoma approaches closely the typical brain. The seg- 



^ Many of these results were presented in the Biological Section of the 

 American Association, September, 1884. 



2 Preliminary Observations upon the Brain of Ampliiuma. Proc. Phila. 

 Acad. Nat. Sc, July, 1883. 



