MONOGRAPH OF THE GENUS STROPFIIA. 
133 
9 
I wish to emphasize the assertion, made before, that no one species 
of Strophia, with rare exceptions, is found on different islands, unless 
recently transported by commercial intercourse. Two instances where 
this has occurred, are in S. copia and S. intermedia, and I must now re- 
cord another. Among the Strophias belonging to the Smithsonian In- 
stitute are a lot of undoubted S. inflata, labelled as coming from Exu- 
lna, the type being from the Bryant collection, taken at Salina Point, 
Auklin Island, 100 miles distant. 
Of course in making the above written statement I do not wish to 
be understood to say that simple geographical bounderies constitute spe- 
cific rank. As shown in many instances, Strophia is an exceedingly 
plastic genus; that is, for some reason, now beyond our knowledge, spe- 
cies become evolved quite readily, and in conformity with a law of evo- 
lution, most readily toward the center of the greatest distribution of the 
species. Hence it is, that if by any chance, some members of a species 
become isolated, either by being transported to a separate island, or to 
some section of the same island where they are isolated by the surround- 
ings, and as pointed out already under the habits of S. nana, compar- 
atively little is necessary to so isolate them, they are apt to speedily 
assume specific characters. This is, prehaps, caused by different envi- 
ronment, different food, or possibly wholly by an inherent tendency to 
vary from the parent stock. 
As shown, especially under observations in S. copia, there is a 
great tendency to assume forms, under apparently the same environ- 
ment, and these forms generally indicate the specific characters that 
will be assumed by isolated individuals. For example, I find that a- 
mong a large series of S. incana from Key West, some few individuals 
which show faint indications of brown fieckings, and Dr. Dali writes me 
that in the Smithsonian collection are specimens of undoubted S. inca- 
na that are flecked. Now this is exactly what I should expect to see, 
for it is in perfect accordance with the law of evolution of which I have 
been speaking, and clearly indicates the flecked S. fasciata found at 
Key Yaccas. 
Now through the operations of the well known law of reversion, ( a 
law too much ignored by naturalists practically, although generally rec- 
ognized by them, ) individuals among nearly all species, especially if 
recently evolved, will show a tendency to revert toward the parent stock; 
this is eminently true in Strophia, and to this cause, in connection with 
the foreshadowing of species, explained above, is due much of the ap- 
parent confusion in many species which are closely allied, but really 
distinct. 
