146 EVOLUTION AND DISEASE. 
similarly affected. In such cases as this it is easy to 
argue that such conditions are reversions to the webbed 
feet and hands of aquatic mammals, but careful con- 
sideration leads me to take an opposite view. If all 
the fingers and toes were furnished with a web we 
should be justified in regarding the phenomenon as 
atavistic, for in their early stages our fingers are com- 
pletely webbed, but later the digits grow at a greater 
rate than the web, until the skin-fold reaches no lower 
than the middle of the first phalanx. This would lead 
me to regard the abnormal union of fingers and toes by 
skin-folds as a sport or spontaneous variation, and not 
atavistic; and this opinion is strengthened by the cir- 
cumstance that, as we have just seen, a patagium may 
form between the thigh and leg, a situation where such 
a web cannot by any possible means be classed among 
atavistic phenomena. 
In order to show to what absurd conclusions loose 
modes of reasonings lead, reference may be made to 
the abnormality of the stomach known as congenital 
or hour-glass contraction. In such cases the human 
stomach is divided by a constricted or narrow portion 
into two compartments (fig. 81), and this has induced 
a few observers to regard this as a reversion to the 
complex stomach of the ruminant, especially the two- 
chambered stomach characteristic of the genus Cervulus. 
There is, however, the following difficulty in accepting 
this explanation. All such deformed stomachs have 
been observed in adults; no one has ever found a 
double-chambered stomach ina child. Again, in many 
of the specimens evidence of disease, such as ulcers, 
old and recent, or scars have been detected in the 
