1040 



It seems as if ventral axones coming from the spinal cord end 

 in it. This caudal tract consists of thin fibres provided with onl}' 

 a small myeline sheath and makes the impression of being ascending 

 in character. 



Whether thi-s can be a primitive homologue of Hellwig's triangular 

 tract, which occupies a similar position in the mammalian cord and 

 oblongata, cannot be said. 



It is interesting to see that this structure is already so well devel- 

 oped in the young Lepidosteus. 



Droogleever B^ortuyn has not indicated its limits in his map of 

 x\mia. It has neither been possible to me to mark its limits with 

 any amount of exactness in this animal. The structure is so diffuse 

 and little circumscrij)t in Amia that its exact topography cannot be 

 given in Weigert or van Gieson preparations. It is certainly smaller 

 and less pronounced, which is not astonishing since Acipenser and 

 Lepidosteus are excellent swimmers and Amia leads a more quiet 

 life, as is also indicated by its name "mudfish". ') 



Resuming my results concerning the arrangement of the motor 

 roots and nuclei in Acipenser and Lepidosteus, and comparing them 

 with Amia on one side and with Scyllium and Tinea on the other, 

 I may conclude: 



Amia Calva, Acipenser and Lepidosteus osseus resemble each other 

 closely, and differ as well from the Selachii as specially from the 

 Teleosts. 



They differ from the Teleosts by the very dorsal position of 

 the motor VII nucleus and by the continuity of the motor 

 column of the Ml, IX. and X nuclei, by the less ventral position 

 and more diffuvse structure of the abducens nucleus, the entirely 

 dorsal position of the V nucleus and the little ventro-medial migra- 

 tion of the oculomotor nucleus. On an average they resemble much 



') ■ I will call altenlion to the possibility that the nucleus paramotlianus of 

 (islies is i-alhci' the liomologue of the ventio-medial accessory olive than of the 

 regular oliva inferior (comp. also Kappers, Folia Neurobiologica Sommerergan- 

 zungsheft, Bnd. VI, 1912) on account of the fact, mentioned by Brouwer (Archiv. 

 Psych. Bnd. 51), that the ventro-medial accessory oUve lias connections with tlie 

 vermis cerebelli, not with its hemispheres, and that the cerebellum of sharks and 

 other fishes is probably the homologue of the vermis. 



It is an interesting fact that this ventro-medial accessory olive of mammals 

 enlarges greatly in cetaceans, where it is again the dominating part of the inferior 

 olive (comp. Kankeleit, Zur Vergl. Morphologie der unteren Saugetier-olive, Inaug. 

 Diss. Berlin 1913). Tiiis, and the fact that in fishes it is probably the only part 

 of the inferior olive that occurs, might lead us to believe that tlie ventro-medial 

 accessory olive is chiefly related willi the musculature of the trunk and the tail. 



