THE SENSE-ORGANS 



477 



and is of still greater interest for its direct connection with the 

 hypophysis, which develops from it. // in this may be seen 

 the remains of an earlier entrance into the alimentary canal, 



FIG. 129. Median sagittal sections through the head of two stages of 

 the Ammoccetes embryo of Petromyzon. [After von KUPFFER.] 



/, II, III, the .three primary cerebral vesicles; d, intestine (mesodaeum); 

 m, mouth cavity (stomatodaeum) ; nc, notochord; ep, epiphysis; hy, hypophysis; 

 hy', portion detached from distal end of hypophysis; rg, olfactory pit; /<?, median 

 olfactory lobe; ch, optic chiasma. 



