FIG. 49. Transverse section from the same series as Figs. 47, 48, but through 

 the outer eyes, the optic lobes, and the hyomandibular suspensorium on the inner 

 or adjacent sides of the twin heads. Below, in the middle line, is the septum 

 between the two mouth-openings, and in it the inner or adjacent Meckel's 

 cartilages. The moulding of the adjacent united periotic capsules and of the 

 otocysts is extremely interesting. See also the two following figures. Other 

 references are given under PI. I. fig. 6, and the plane of section is indicated by 

 line 49 in PI. XXI. figs. 91-93. (xiS.) 



FIG. 50. Transverse section from the same series as the last three figures, but 

 through the posterior part of the optic lobes, the commencement of the iter, the 

 inner hypoaria, the entrance of the optic nerve on one side, and the back part of 

 the mesial oral septum containing the united adjacent hyoids. Other references 

 under PI. I. fig. 6. (xi8.) 



FIG. 51. Transverse section from same series as the last four figures, but 

 through the outer auditory organs and the posterior part of the brain, which is 

 obviously made up of two converging medullae. The notochord is double, and 

 the inner parachordals have a small mesial mass of muscle wedged in between 

 them. Compare this section with PI. IV. fig. 18 (normal), and with PI. IX. fig. 38 

 (union at optic lobes). Other references under PI. I. fig. 6, and plane of section in 

 PI. XXI. figs. 91-93, line 51. ( x 18.) 



PL. XIV. 



