FIG. 37. Transverse section from same series (double monster 

 with union at optic lobes) as that illustrated in the two preceding 

 figures. The section is further back than in Fig. 36. Evidences of 

 duplicity are disappearing, but some are still to be made out, e.g. 

 two sets of infundibular downgrowths in the floor of the brain, and 

 two pairs of trabeculae, of which the inner, or adjacent, units have 

 united to form a mesial bar separating the two pituitary spaces. 

 Compare with PI. III. fig. 16 (normal) and with PI. XIV. fig. 50 

 (union at medulla). Other references under PL I. fig. 4 and plane 

 of section in PI. XXI. figs. 88-90, line 37. ( x 20.) 



FIG. 38. Transverse section from same series as in the last 

 three figures, but passing through the back part of the head. It 

 is remarkable that the evidence of duplicity here is greater than 

 in the preceding section. The two notochorcls are widely separated, 

 and are surrounded by a mass of cartilage representing both pairs 

 of parachordals. There is a median series of muscle segments 

 representing the fused adjacent somites. The heart cavities, how- 

 ever, form a single series. Compare with PI. IV. fig. 18 (normal) 

 and with PI. XVII. fig. 57 (union at medulla). Other references 

 under PI. I. fig. 4, and plane of section in PI. XXI. figs. 88-90, 

 line 38. (xjo.) 



PL. IX. 



