2^6 Susanna Phelps Gage 



THE BRAIN IN EMBRYOS. 



The incubation of ova in the laboratory lasted about one 

 month. Within seven days, the optic and otic vesicles are 

 formed. At twelve days the eyes, lens and rudiment of a 

 nasal pit are formed and the brain in reconstructed mesal view 

 agrees well with a figure of a newt shown by Misses Johnson 

 and Sheldon (29). The partition between the prosen- and 

 diencephal is formed and from this extends the dorsal division 

 between the hemicerebrums. At fifteen days a protuberance of 

 the diencephal (epiphysis) is formed and the infundibular re- 

 gion is partially constricted. No alba has appeared, the walls 

 being purely cellular. A mesal view is similar to one by His 

 (27) of Ambhy stoma pundatum. At or near the time of 

 hatching the eyes are large ; the muscular development is ex- 

 cellent and suited to the quick darting motions. The yolk sac 

 is large and the mouth not yet perforated. Balancers exist 

 and the nasal pit is formed. The cephalic curvature still re- 

 mains so that a transection in the cephalic region still shows 

 the structures found in frontal sections of older forms. The 

 united cerebrum and olfactory lobes are short, extend ventrad 

 from the diencephal, which with the mesencephal forms the 

 most cephalic and the most prominent portion of the brain. 

 In the wall between the hemicerebrums, is the rudiment of the 

 paraphysis (Fig. 73) and into the diacoele projects a rudiment 

 of the diaplexus. In figure 74 the aula is seen to reach 

 nearly to the tip of the rhinencephal. The mesocoele is a wide 

 cavity, the lateral recesses of the epicoele are formed, and the 

 lateral masses of alba are considerable, while, except in the 

 medulla, little alba is seen on the meson. Within two da}'S 

 after hatching the cranial flexure has nearly disappeared. 



BRAIN OF OLDER \,KSM M, AND OF RED FORMS. 



Before the end of aquatic larval life the general longitudi- 

 nal proportions of the adult brain are attained, but the parts 

 are more depressed dorso-ventrall}' while the cavities are 

 large. This appearance increases until the middle red stage 

 and corresponds with the general appearance of loose struc- 



