1402 
to explain this range of malformations, in the same way as Kunprat did. 
Different efforts have been made to explain the designed monstra, 
and they can be divided into two groups. 
In the first group those belong try to interpret the monstrum, 
by accepting a minus of germ material causing it. 
If there was a developing embryo with insufficient germ material 
at the medio-ventral end of the frontal pole, then the medio-ventral 
end of the brain (arhinencephalia) and skull would not or only 
insufficiently be developed: Then the laterally placed eye vesicles 
will approach each other; eventually they will even confluate (their 
medial parts being undeveloped). 
This conception accounts for the frontal arhinencephalia and the 
missing of the sagittal separation at the frontal pole of the hemisphere. It 
also accounts for the possibility of a gradual range of the monstra, 
from the cebocephalia to the complete cyclopia. 
The most difficult part in such hypothesis, is to give a plausible 
interpretation of the dorsal sac. For if it may be granted, that a secon- 
dary hydrocephalus often accompanies different anomalies of the 
brain, the hydrocephalus localised at the roof of the IIId ventricle, 
and always there, is indeed extraordinary. 
It is necessary to desire an explanation, why in eyclopian monstra 
the hydrocephalus always prominates the roof of the III" ventricle, 
and is often found only there. Such a conception of the cyelopia 
does not need a fixation in time for its commencement. There is 
no germ-material, therefore the tendencies for development are missing 
to form the medio-ventral part of the frontal pole of the embryo. 
This attempt of interpretation is mostly accepted by investigators, 
hoping, that the study of monstra may throw some light upon the 
history of developments of partly insufficient brains. They are not 
inclined to make use of pathologie influences in teratologic problems 
and avoid as long as possible to accept that such influences may 
play a role in their formation. 
The second group of attempts to interpret cyclopian monstra grants 
an influence to pathologic instances. Their defenders however differ 
in many ways. 
The developing embryo may lose in an early stage — e.g., when 
the eye-vesicles begin their differentiation, the original prosence- 
phalon being not yet divided by a sagittal fissure — the medio-ventral 
part of the frontal pole. By many experiments, e. g. by cutting away 
precisely medially a small piece out of the embryonal shield in 
fundulus, Lewis succeeded in transforming the development of this 
little fish into acyclops monstrum ; also Srockarp reached the same 
