FlG. 52. — Horizontal section of double trout monstrosity belonging 

 to the type illustrated in PI. II. figs. 7, 8 (union in pectoral region). 

 Adjacent pectoral fins are not present. 1 he section passes through 

 the optic lobe masses, the cerebellum, and the upper parts of the 

 periotic cartilage? in either head, while, further Lack, the spinal cord 

 is seen to have its central cavity much dilated and bifurcating into the 

 two fourth ventricles. Compare with PI. V. fig. 21 (normal), and with 

 PI. X. fig. 39 and PI. XII. fig. 43 (union at optic lobes). For other 

 references see under PI. II. fig. 7. ( X20. ) 



I i'.. 53. Horizontal section belonging to the same series as 

 Fig. 52, but at a slightly deeper level. The section passes through the 

 cavities of the pineal bodies, of the optic lobes, the iter, and fourth 

 ventricle. \- in Pis. X.-XII. figs. 39-46, owing to the curvature of 

 Q, the trunk i-, cut through obliquely. The section here 

 shows the composite spina! cord, the two outer series of mi 



j in ins, and a mesial similar series between the two notochords. 

 I >r other references see under PI. II. fig. 7. ( x 2 o.) 



PL. XV. 



