36 MALL. [Vov. XIX. 
much as it underwent histolysis and cytolysis. The epider- 
mis also showed changes; instead of being smooth on the 
outside it became rough, grew up into numerous papillomata, 
as Bardeen found in his X-ray larve, and as I have often 
found in pathological human embryos. 
Hertwig explained Morgan’s remarkable experimental 
production of spina bifida by assuming that the concentration 
of the salt retarded the growth of the cells of the egg and 
that the reduction of energy is unequal in different portions 
of the egg. Through this change differences in the rate of 
growth are established unlike those in the normal embryo, 
which naturally ended in the production of an abnormal 
embryo, that is, a monster. In this instance Morgan’s sodium 
larva is the typical embryonic stage of spina bifida. 
The spina bifida, although complete at first, rarely remains 
so, for the neural tube closes more or less, remaining open 
usually behind and often in front, giving quite typical speci- 
mens of anencephaly. It is clear, therefore, that this variety 
of spina bifida is also due to an arrest of development 
which could easily undergo secondary changes and produce 
a condition which is often found in foetuses at full term. 
Hertwig concludes, properly so, I think, that every human 
ovum has within it the power to develop into a monster, 
either anencephalic or otherwise, and that it is not due to any 
abnormal condition of the germ, but to external influences 
which affect the growth of the egg. A monster is due to the 
influence of external substances which retard the growth of 
the embryo, usually one portion more than the other. For a 
long time teratologists have practically stated the same in 
recognizing that monsters usually represent arrestments of 
normal development. Not only is this true regarding mero- 
somatous monsters, but every egg has within it the power 
to develop into a polysomatous monster, or into duplicate 
twins. 
Later Hertwig® extended Morgan’s experiments to Axolotl, 
thus making it applicable to at least six species of animals. 
"Hertwig, Gegenbaur’s Festschrift, II, 1896. 
