EARLY DEVELOPMENT OF HEMISPHERES 291 
preceding and during the evagination of the hemisphere. The 
wall of a neural tube of a stage-30 larvae just before the beginning 
of the outpouching does not show clearly the primary lamination 
of Herrick. It is not until the telencephalic evagination is com- 
pletely defined (about stage 40) that the four divisions of the 
cerebral hemisphere become obvious. We may say, then, that 
the cerebral hemisphere develops as a result of the evagination of 
the relatively undifferentiated alar plate of the neural tube, ceph- 
alad of the sulcus limitans and ventrad of the sulcus diencephal- 
icus medius, and that the lamination subsequently developed is 
imposed on this primitive arrangement by factors operating 
through the growth of the embryo. It is evident, then, that the 
primitive laminae as described by His become to some extent 
obliterated by the secondary lamination which Herrick has de- 
scribed. In other words, the structural arrangement of the ner- 
vous system common to all vertebrates, as His described it, is 
modified in Amblystoma by the acquisition of the further rear- 
rangement described by Herrick. 
The fundamental lamination of His is not, however, entirely 
obscured. Owing to the sharp ventral curvature of the sulcus 
limitans to end in the preoptic recess, the dorso-ventral .lamina- 
tion (in the sense of His) of the neural tube caudally, becomes 
antero-posterior in the cephalic portion. Some evidence of the 
persistence of this arrangement is seen in the fact that a sensory 
nerve (the olfactory) enters the brain near its cephalic terminus 
to be followed by a correlation area discharging caudally into 
the motor area of the hypothalamus, an obvious antero-posterior 
lamination. But it is likewise just as evident that this antero- 
posterior relation has given way to, or been dominated by 
a subsequent dorso-ventral lamination imposed on the funda- 
mental nervous structure. In other words, we find that, follow- 
ing the evagination of the hemisphere, the four primary laminae 
of Herrick are superimposed at right angles on the primary col- 
umns of His in the rostral portion of the neural tube. 
One of the interesting facts Herrick discussed in his 1910 paper 
was the continuity of the columns of the telencephalon with 
homologous areas in the diencephalon. The two ventral lami- 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 34, NO. 3 
