88 EMBEYOLOGY OF THE LOWEE YEETEBEATES oh. 



Fig. 53. — Camera tracings of sagittal sections through the brain of Lepidosiren 

 at successive periods of development. 



Figs. A to F are drawn under the same magnification, Fig. G under a lower magnification. A, stage 

 25 ; B, stage 28 ; C, stage 29 + ; D, stage 31 ; E, stage 35 ; F, stage 38 ; G, adult in second year. 

 a.c, anterior commissure ; cer, cerebellum ; c. H, cerebral hemisphere ; eh, optic chiasma ; /, primitive fold 

 of brain-floor ; Kg, ganglion habenulae ; K.c, habenular (superior) commissure ; i.g, infundibular gland ; 

 inf, infundibulum ; par, paraphy.sis ; pin, pineal body ; p.c, posterior commissure ; l.p, choroid plexus of 

 lateral ventricle ; t.o, tectum opticum ; * originally anterior end of brain-floor. Structures occurring not 

 in the sagittal plane but in sections parallel to but some distance from it, are shaded with oblique lines. 



