256 HENRY C. TRACY 



Fig. 17 A drawing from the same section shown in figure 15, but with higher 

 magnification to show the relations of the three divisions of the macula acustica 

 utriculi. The plane of section passes at the extreme lateral end of the posterior 

 division of the macula. The septum of the anterior osseous capsule is only 

 slightly developed at this stage and is not visible in this section. The relation 

 of the anterior and middle divisions of the macula to the two divisions of the 

 utricular subcerebral canal arc well shown. 



Fig. 18 Section of the anterior and middle divisions of the macula to show 

 the structure of the otolithic membrane. Stolephorus mitchilli, 8 mm. in 

 length. At this stage the divisions of the macula are in the process of differen- 

 tiation from a single sensory spot. Section drawn as viewed through the binocu- 

 lar microscope, 1/12 oil-immersion lens. The otolithic membrane is slightly 

 diagrammatic. 



Fig. 19 Drawing from the same slide as figures 15 and 17 to show the details 

 of the anterior and middle division of the macula acustica utriculi and of the 

 otolithic membrane; 1/12 oil-immersion lens. 



Fig. 20 Section of the otolithic membrane approximately parallel to its 

 surface. Brevoortia tyrannis, 25 mm. in length, I, 6 objective. This shows the 

 sections of the 'cells' or chambers in the membrane. They are cut transversely 

 in the middle of the section, but appear oblique at cither end owing to their 

 change in direction. 



