4 
Larvae 25-26 mm. September ist. The normal larvae measure 
25-26 mm. from the end of the snout to the tip of the tail. The 
general form of the body and the degree of differentiation of external 
structures in the normal are shown in Fig. 4. At this time the gills 
show the same differences as recorded in the preceding stage in that 
those of the decapitated larvae are shorter and thicker and the gill 
filament more irregularly placed than in the normal. The limbs show 
the same degree of differentiation, four toes being present in both 
normal and decapitated. 
A series of careful measurements was made as follows: Average 
length of ten normal from tip of tail to anterior margin of the 
anterior gills, 25 mm. Average length of nine decapitated 23.5 
mm. Length of trunk from center of the base of the anterior 
limb to the center of the base of the posterior limb, normal 
13 mm., decapitated 11.5 mm. Length of tail from center of posterior 
limb, normal 12.5 mm., decapitated 11 mm. Length of limbs spread 
from tip to tip, normal 8 mm., decapitated 8.5 mm. Length of posterior 
limbs spread from tip to tip, normal 6.5 mm., decapitated 7 mm. 
Diameter of trunk from side to side midway between limbs, normal 
3.75 mm., decapitated 4 mm. Diameter of trunk midway between 
limbs dorsoventral, normal 4.5 mm., decapitated 5 mm. Length from 
tip to tip of gills distended, normal 6.25 mm., decapitated 6 mm. 
The measurements recorded in the preceding paragraph show 
that the yolk absorption is less rapid in the decapitated than in the 
normal and as a result the general growth of the animal is somewhat 
retarded; excepting in case of the limbs which in the decapitated are 
slightly in excess of the normal. It may be said that all the surface 
structures differentiate in the same sequence as in the normal. On 
the whole the study of surface changes show that the portion of the 
brain removed has but little trophic influence on the growth and 
differentiation of organs. 
Movements. 
The normal larva of 15-16 mm. when removed from the sur- 
rounding envelopes moves only at long intervals, but when stimulated 
mechanically it immediately responds and the contractions are ob- 
served to begin in the myotomes just back of the anterior limb buds, 
from which locality they proceed in serpentine manner until they 
reach the level of the posterior limbs where they cease. 
