Zoology. — "The Fore-brain of Si/nbrau,chidae". Hy Dr. C. J. 

 V. u. Horst, Amsterdam. (Commuiiicated by Prof. Max Wkber). 



(Communicated in the meeting of May 26, 1917). 



The Synbranchidae are distinguished from ail other Teleosts by 

 a secondary coalescence of the two halves of their fore-brain. 



In the rich collection of the Central Institute for Brain Research 

 at Amsterdam, which includes almost all the suborders of the 

 Teleostei, I found several representantives of other suborders of Teleosts 

 in which the hemispheres of the fore-brain are pressed together, 

 but where no coalescence has occurred. 



In only one of the three series of Hippocampus in the Institute the two liemis- 

 pheres partially have grown together in the midline, dorsal from the commissura 

 anterior. This, however, must be regarded rather as an abnormality in this specimen 

 caused by the presence of parasites in the brain cavity, whereby the fore-brain 

 has become totally changed in form. 



Of the suborder of Synbranchii, I was able to examine the brains 

 of Monopterus albus (Zuiew) received from Dr. Sunier of Batavia, 

 and of Synbranchus marmoratus BL, which I obtained from the 

 Aquarium of the Royal Zoological Society "Natura Artis Magistra" 

 at Amsterdam. The brains of these tlshes were cut in series of 

 sections 20f.t thick, treated by the Weigert-Pal method and contra- 

 stained with paracarmine. 



Monopterus and Synbranchus are exactly alike as regards the 

 formation of the brain, as I have pointed out in a previous paper (2). 

 The coalescence of the two hemispheres is therefore not an abnorm- 

 ality here as in the above-mentioned specimen of Hippocampus, 

 but is a typical characteristic of the family of Syubranciiidae, and, 

 if it also occurred in Amphipnous, even of the whole order of 

 Synbranchii. 



The outer form of the fore-brain. 



The tila olfactoria are collected in a short nervus olfactorius which 

 forms a fairly shar[) boundary with the bulb. 



As in most of the Teleostei the buibi olfactorii in Monopterus 

 and Synbranchus are sedentary; an elongated tractus olfactorius is 



not found heie. 



15 

 Proceedings Royal Acad. Amsterdam. Vol. XX. 



