182 PATTEN. [Vot. II. 
EXPLANATION OF PLATE IX. 
Fic. 19. Cross section of the cephalic lobes of an embryo somewhat younger than 
that in Fig. 1, Pl. VII. X 360. 
Fics. 20-23. A series of cross sections through the cephalic lobes of an embryo 
like that in Fig. 1; showing the three ganglionic invaginations. X 360. 
Fics. 24-27. Cross sections of an embryonic head about same age, perhaps 
younger, as that in Fig. 1. This head was abnormally shaped. It was deeply invag- 
inated along the median line; on the sides of the invagination were the antenne, and 
at the bottom, the mouth. X 360. 
Fics. 28-34. A series of cross sections through the head represented in Fig. 5. 
They show the structure of the brain, optic ganglion, and optic plate. X 360. 
FIGs. 35, 36. Cross sections of a head like that in Fig. 6, just after the optic gan- 
glion is completely shut off from the exterior. X 190. 
Fics. 37-39. Cross sections of a younger stage than that in the preceding figures, 
showing the last stages in the enclosure of the optic ganglion, etc. X 138. 
Fic. 40. Semi-transparent surface view of the optic ganglion and one side of the 
brain; showing the three lobes of the optic ganglion, the medullz, and the nerves. 
Fic. 41. Semi-diagrammatic horizontal section through the medullary portion of 
the optic ganglion; showing the position and shape of the medullz and the nerves 
that unite them with their respective eyes. 
