150 HALSEY J. BAGG 
marked absence of the cerebral cortex until only a very thin 
lamina of tissue remained to represent that structure, and there 
were large areas in the frontal, occipital, and temporal region 
where no cortex existed at all, so that when the meninges were 
removed the basal ganglia were clearly seen from without. 
This correlation between defects in the development of the eye 
and the brain has been emphasized by Stockard (19) in his recent 
paper on developmental rate and structural expression. He 
states as follows: ‘‘The periods of arrest necessary to induce 
the eye and the brain modifications are so close together or so 
nearly the same, that one generally finds combinations and mix- 
tures of the defects among the same experimental group of 
embryos.’’ Again in the same article Stockard has shown that 
the type of deformity that results from experimental disturbance 
depends upon the developmental moment at which the imter- 
ruption occurs. It is significant that the animals of this experi- 
ment showed arrests in the development of the neopallial portions 
of the brain and not in those regions which are ontogenetically 
older. Apparently the radium emanation, acting towards the 
end of pregnancy, had affected the development of the brain 
after the basal ganglia, the cerebellum, and medulla had become 
fairly well differentiated, and therefore those portions showed no 
gross changes. But the radium had slowed the developmental 
rate of the neopallium (which we know is one of the last portions 
of the brain to differentiate) during its period of active cell pro- 
liferation, and that portion of the brain was never able to reestab- 
lish its proper rate of development in relation to the other parts 
of the brain. If the period of treatment had occurred earlier in 
prenatal existence, other portions of the brain would probably 
have shown disturbances as well. The writer does not believe 
that the deformities in the brains of these animals were due to 
the early production of vascular disturbances later recovered 
from, but to an actual inhibitory effect of the radiation upon the 
developing nerve cells. If extravasations had occurred in this 
group of animals, and were so situated as to affect the develop- 
ment of the cerebral cortex in particular, they probably would 
have been detected as were even the comparatively small lesions | 
