6o2 'Journal of Comparative Neurology and Psychology. 



2. The Position and Character of the Cells of Origin. — In all 

 fishes and amphibians studied the cells of origin are located in the 

 tectum mesencephali, the majority of them near the median line. 

 They are always massed along the median line without apparent 

 bilateral symmetry or any other regularity of arrangement. In the 

 selachians they are often piled two or three deep at the median line. 

 Laterally they form a single row or are scattered, an occasional 

 cell being found at the extreme border of the proper roof portion 



Fig. 4. Cells of origin of the radix mesencephalica in the locus coeruleus of 

 the rat. A is farther mesad and cephalad ; B, farther caudad and laterad. 

 In B two cells send their processes caudad (toward the left). 



of the tectum (Fig. 6). In Scyllium and Squalus they extend 

 throughout the entire length of the tectum and the greatest number 

 of cells is found at the posterior part of the tectum. In Scyllium 

 stellare there is an especially large group which extends into the 

 medullary velum so that several cells lie beneath and behind the 

 crossing fibers of the IVth nerve. In Acipenser the cells are to be 

 found only in the anterior part of the tectum, the majority of them 

 in the immediate vicinity of the posterior commissure (Johnston, 

 1901). In Araia embryos and young up to 25 mm. in length, the 



