490 CLASSIFICATION. 
Such questions cannot receive at present any satis- 
factory answer, but the evidence we have seems to 
indicate that pre-existing forms were simpler, and less 
specialised in structure than those now existing, and 
hence if we meet with malformations of a simple kind, 
we may consider them as possible reversions ; while, if 
they present features of increased complexity, and 
more sharply defined differentiation, we may assume 
them to be evidences of a progressive rather than of a 
retrogressive tendency. 
That monstrosities so called may become the starting 
points of new forms is proved by the circumstance that, 
in many cases, the peculiarities are inherited so that a 
new “race” is produced and perpetuated: and if a 
new race, why not a new species? The difference is 
one of degree only. 
