544 C. JUDSON HERRICK 



EXPLANATION OF FIGURES 



73. A diagram similar in plan to that of fig. 72, reconstructed horn actual sec- 

 tions of the cyclostome brain, Ichtnyomyzon concolor. It is based on the same 

 seiies of cross sections illustrated by figs. 74 to 81 and the planes of the sections 

 figured aie indicated on this figure. (See the text, pp. 470, ff.) 



74 to 81. A series of cross sections through the forebrain of a specimen of Ich- 

 thyomyzon concolor (Kirtland) 120 mm. long. Drawn from haematoxylin prepar- 

 ations made by Dr. Charles Brookover. X 30. The plane of each of these sections 

 is indicated on fig. 73. The series of sections is numbered, beginning with no. 1 

 at the lamina ;erminalis and the serial number of each section figured is given in 

 the following descriptions, the sections being 15 m thick. Cf . the series of cross- 

 sections of Lampetra figured by Johnston, '02. 



74. Section no. 3, immediately behind the lamina terminalis. 



75. Section no. 4, through the recessus preopticus. 



76. Section no. 7, through the rostral end of the optic chiasma. 



77. Section no. 13, at the rostral border of the interventricular foramen. 



78. Section no. 17, immediately caudad of the foramen and passing through the 

 probable site of the embryonic velum transversum. 



79. Section no. 23. This section is wholly diencephalic except the lateral hemi- 

 spheres. The dorso-median ridge here attains its greatest size. 



