8 
POPULAR SCIENCE REVIEW. 
flowers ; or at all events this hypothesis is entirely inconsistent 
with the theory of development by Natural Selection only. 
There is doubtless an apparent object in the one case which we 
are unable to detect in the other ; but this does not seem to 
me sufficient reason for giving a different name to the pheno- 
menon itself. 
Professor Thistleton-Dyer objects to the application of the 
term “ Mimicry ” to the case of closely resembling plants, on the 
ground that we do not here find the imitative species occupy- 
ing the same area as occurs in the animal kingdom. The 
instances I have given above will show, however, that his 
statement that “ the resembling plants are hardly ever found 
with those they resemble ” is a far too general one. Professor 
Dyer has made a useful suggestion in proposing the terms “homo- 
plastic” and “ Homoplasy ” (first applied by Mr. E. E. Lankester 
to external resemblances in the organs of animals) to the class 
of phenomena under discussion. The term is a good one, as 
simply expressing a fact and not a theory, and is free from the 
objection I have mentioned above to the use of “Mimicry.” 
One explanation of Mimicry or Homoplasy in plants that 
has been suggested is that it is due to consanguinity or 
heredity; and a writer in “ Nature ” has even been bold enough 
to offer this suggestion to account for the resemblance between 
a Thujopsis and a Seiaginella already referred to. But the 
value of the theory of hereditary reversion is entirely destroyed 
if it is strained in this manner. It is true that some botanists 
have traced a genealogical affinity between Conifers and the 
higher Cryptogams; but the relationship is at the best a very 
remote one ; and to attribute the external facies of a Conifer 
to its alliance with a Lycopodium is as wild as to attempt to 
account for the varied colours of birds by their affinity to 
insects, or of snakes from their alliance with fishes. To be con- 
sistent, this theory ought to be applied to the animal kingdom 
also, and is a hundred times more to the purpose as an expla- 
nation of mimetism among Lepidoptera. We may compare 
with this unnatural straining of a theory the truly scientific 
manner in which Mr. Darwin applies the principle of heredity 
to account for the occasional occurrence of stripes on the hind- 
quarters of the horse from its affinity with the zebra. If, 
however, hereditary reversion acts as remotely as has been 
suggested, this no more proves the horse to be related to the 
zebra than to the hyaena. 
A certain class of general superficial resemblances may 
undoubtedly be attributed to the action of natural external 
causes, to a similarity of conditions of growth ; and to these I 
have already sufficiently alluded. This explanation is, how- 
ever, entirely inadequate in the case of the minute resemblances 
