4 | C. W. M. Poynter 
ing to lower types or not. If the anomaly is found in some form 
below man it is retrogressive, if not it is progressive. This 
is as far as comparative anatomy can carry us, but compar- 
tive embryology has thrown more light on the subject. Meh- 
nert (1895) has suggested a new significance for the variations 
in the embryo. These variations are of themselves of great 
theoretic interest, they furnish us with a hint of the growth 
processes and are not apparently confined to the phylogenetic 
processes. This consideration of embryonal variations would 
suggest a third class of variations according to Mehnert, “Als 
Ungluchheiten in der Art der Entwicklung eines Organs inner- 
halb derselben Species oder mehrfach vertretener Organe inner- 
halb eines Individuums zusammenfasst.” 
~ When we find in man a condition similar to that found in some 
lower animal we may assume that the same factors were operative 
during a certain stage of development which are constant for 
that animal. This only suggests that at times during develop- 
- ment man may be subject to unknown forces which are constantly 
operative in the lower forms. Objection to the assumption that 
variations dissimilar to conditions found in lower forms are pro- 
gressive may be made on the ground that we are too near to 
judge. 
Of the remote causes of variation we know nothing yet and 
if we assume that at a certain time unusual factors operate in a 
human embryo to produce a variation we are still ignorant as to 
what the factors are. With increased knowledge of development 
the number of anomalies which may be considered as indicative 
of atavism decrease. 
Another feature of variation has been suggested by Keith 
(1895), who says: “An extended observation will probably show 
that nearly allied races are more emphatically distinguished by 
the kind and frequency of their anatomical variations than by 
what would be described as their typical structure.” If this were 
known to be true we could only speculate as to its significance. 
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