577 



entwickeln sich aus ihnen durch einen Faltungspro ceß die Genital- 

 organe, so daß sie dann schließlich auch die Function von Leitern der 

 Geschlechtsproducte haben. Sowohl der Bau der Excretionsorgane 

 als auch die Bildung des Genitalapparates und die Entwicklung der 

 Sexualproducte ist bei den Priapuliden demnach völlig verschieden 

 von den andern Gephyreen, wodurch eine ziemlich weite Kluft 

 zwischen ihnen geschaffen wird, so daß das System derselben hierdurch 

 vielleicht modificirt werden müßte, wie es ja bereits von Hatschek 

 versucht wurde. 



6. Note upon the cerebral commissures in the lower Vertebrata and 

 a probable fornix rudiment in the brain of Tropidonotus. 



By Dr. Henry F. Osborn, Princeton, New- Jersey, U.S. A. 



eingeg. 12. September 1886. 



The further study of the cerebral commissures has confirmed in 

 most particulars the observations which I published in an April 

 number of the Zoologischer Anzeiger^. 



The corpus callosum is present in the Amphibia and Sau- 

 ropsida. From the close homology between the Amphibian and Dip- 

 noan brain, observed in Protopterus by Rabl-Riickhard and Fulli- 

 q u e t s, and by myself in an embryo Ceratodus, I anticipate that the 

 corpus callosum will also be found in the Dipnoi and fthat in these 

 forms we shall be able to trace the transition to the commissura 

 interlobularis in the brain of the lower fishes. This is probably 

 homologous with both the anterior commissure and corpus callosum. 



The pars olfactoria of the anterior commissure seems to be 

 wanting in the Chelonia [Emys] and Aves [Anas and Columha) but is 

 well developed in the Ophidia [Tropidonotus].^^ Associated with this in 

 the latter genus is a distinct bundle supplying the anterior portion of 

 the hemisphere mantle. This division, which attains a great develop- 

 ment in the Marsupial brain, may be called the pars frontalis. 



The corpus callosum in Emys extends upwards in the inner wall 

 of the lateral ventricle and divides. The larger division spreads over 

 the inner wall, the smaller division extends backwards above the fo- 

 ramen of Monro and downwards along the hippocampal fold. This is 

 homologous with the commissura cornu ammonis. This obser- 

 vation, supported by the development history of the cerebral commis- 

 sures in the Marsupial brain prove that the above commissure is pri- 

 mitively a portion of the corpus callosum and only secondarily united 

 with the fornix. 



See also the Morphologisches Jahrbuch 12. Bd. August. 



