FIG. 39. Horizontal section through a double monster with 

 union in region of optic lobes, and belonging to Class I., i.e. 

 the type illustrated in PI. I. figs. 4-5 (surface views), and in 

 Pis. VIII. -IX. figs. 35-38 (transverse sections). Compare with 

 PI. V. fig. 21 (section of a normal embryo at the corresponding 

 level). The section passes through the upper parts of all four 

 eyes of the two auditory organs. The two forebrains are cut 

 somewhat obliquely, while the large composite optic lobes and 

 their central cavity are seen in horizontal section, as also are 

 the fourth ventricle and the medulla oblongata. Other refer- 

 ences are given under PI. I. fig. 4. ( x 16.) 



FIG. 40. Horizontal section of the same double monster as 

 in last figure, but at a slightly deeper level. The section passes 

 through the middle of the outer eyes, but only through the 

 upper segments of the adjacent eyes. The composite cavity of 

 the optic lobes will be seen to bifurcate in front, and lead into 

 the cavities of the two forebrains. For other references pee 

 under PI. I. fig. 4. ( x 16.) 



PL. X. 



