36 yoiirnal of Coviparativc JSlcuroiogy and Psychology. 



Fig. I. Series L, 120 hrs. D, dorsal lip and mas. barbule group. V, ventral lip group which at 

 this stage contains only one bud that could be considered as on the outer surface. 



Fig. 2. Series O, 146 hrs. V, ventral lip buds. M.B, mental and post mental buds. D' , dorsal 

 lip and maxillary barblet group. B, C, D, subdivisions of nasal group. Subdivision A is not repre- 

 sented on this chart. It is so closely related to the anterior nasal opening that it is not easy to separate 

 it from buds lying on the nasal barblet. 



Fig. 3. Series U, 244 hrs. F.L., Ventral lip. ^<3, mental and post mental barblet buds. D.L., 

 Dorsal lip and maxillary barblet group. A,B, C, D,E, subdivision of nasal group. C and C", ventral 

 and dorsal subdivisions of the opercular group. Subdivisions A and B are not present in this stage. 



Fig. 4. 2oi mm. stage. At this stage the various subdivisions of the nasal group are continuous 

 with each other and reach back to the eye. The dorsal lip and maxillary barblet group is continuous 

 dorsally with the nasal group and the ventral lip and barblet group is continuous posteriorly with the 

 posterior mand. subdivision (B) of the opercular group and dorsally behind the angle of the mouth with 

 the dorsal lip group. None of these buds are shown on the chart except {B). B, the posterior mand. 

 division of the opercular group. C and C, the ventral and dorsal portions of the opercular division. 

 D, the branchiostegal buds. Subdivision ^, which lies behind and under the eye, is omitted. A', B' , 

 the cerebellar and occipital buds. C", the body buds. 



