2 Howard Ayers and Julia Worthington 



including the midbrain, "tweenbrain, and forebrain. This division is 

 fundamental and is present in Amphioxus. The Hindbrain will be 

 described first in this and succeeding papers, each one of its component 

 systems being studied both as a separate organ and in its relation to 

 the other brain organs. The present paper is devoted to a study of the 

 Acustico-lateral system, in both its internal and external relations. 



Methods. 



The material on which this study is based consists of embryos, the 

 young and adult hagfish — species Bdellostoma dombeyi, Lac, — collected 

 by the writers at various times from the Bay of Monterey. The hagfish 

 were caught in traps and kept in healthy condition in a large tank 

 supplied with running salt water. They were taken out as needed and 

 the living tissue treated according to the chosen method. This course 

 was found to be absolutely necessary, as the brain tissue deteriorates 

 very rapidly. When the hagfish Avere caught by hook and line and died 

 in consequence, brains taken from them within two hours after death 

 uniformly failed to give the Golgi reaction. The methods found most 

 satisfactory for the study of the relations of the fiber tracts in the 

 adult brains were the rapid Golgi method and Cajal's absolute alcohol 

 and ammonium-absolute alcohol silver nitrate methods, though good 

 results along certain lines were sometimes obtained by intra-vitam 

 methylene blue staining. The results obtained in these ways have been 

 controlled by brains hardened and cut in situ and stained with carmine, 

 haematoxyline, etc. We have not been able to obtain the characteristic 

 reaction from experiments with the Weigert methods. 



We wish here to express our thanks to Miss Elizabeth Worthington 

 for her kindness in making the wash drawings for Tigs. 47, 48 and 49. 



The Acustico-latekal System. 

 The name acustico-lateral system is given to the group of nerves 

 comprising the two ear nerves, the two lateral line nerves, anterior and 

 posterior, and the acusticus nucleus with its connections to other parts 

 of the brain. The nucleus itself is very different in Bdellostoma from 

 what it is in higher forms, even in its nearest relative Petromyzon. In 

 this latter form (Johnston, '02) the tuberculum acusticum consists of 

 three distinct parts, a ventro-lateral nucleus, a dorso-median nucleus 

 lying close upon it, and, dorsad to both, separated from them by an 



