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POPULAR SCIENCE REVIEW. 
form a correct estimate of the term “ species,” which is indeed the pivot 
whereon the whole argument turns ; and as M. de Quatrefages passes in 
review the various definitions that have been applied to it by the most 
eminent writers on the subject, we shall extract the most important of these, 
representing the opinions of different naturalists. The definition of the term 
has been based upon two distinct phenomena, namely, the resemblance 
between individuals and their descent from similar individuals, or, as the 
author has it, “ resemblance” and “ filiation.” 
To place the inquiry in a clear and comprehensible manner before our 
readers, we will state it thus : — -If there were placed before us two plants or 
animals closely resembling one another, and we were asked to decide whether 
or not they belong to the same species, would it suffice if we compare them 
with other animals; and finding that they resemble one another more closely 
than they resemble any others, we give it as our decision that they belong to 
the same species ? Or is it necessary that we should first inquire into their 
parentage, in order to ascertain whether or not they were descended from the 
same original couple ; and if they were not so descended, must we then 
decide that, however closely they may resemble one another, they are not 
of the same species ? Or if they were, and yet were ever so dissimilar, 
must we pronounce them to belong to the same species ? 
The various replies that have been given to these questions may be found 
in the following opinions quoted by M. de Quatrefages as to what constitutes 
a species : — ■ 
Ray. — Vegetables which have a common origin, and are produced from 
seeds, whatever may be their apparent differences. 
Tournefort. — An assemblage of plants which are distinguished by some 
particular characteristic. 
Buffon. — Species is nothing else than a constant succession of similar 
individuals which reproduce themselves. 
De Candolle. — An assemblage of all those individuals which resemble one 
another more than they do any others ; are able by reciprocal fecundation to 
produce fertile individuals, doing so by the generative process, and in such a 
manner that by analogy they may be supposed all to have been descended from 
one single individual. 
Vogt. — The reunion of all individuals which originate from the same 
parents, and are either themselves similar to the original stock, or became so 
through their descendants.* 
Lamarck only regards “ species ” as a relative expression, and for him it 
has no fixed existence. He believes in the transmutation from one species 
to another, and in the formation of new species, “ through a tendency,” says 
M. de Quatrefages, “ to satisfy certain wants,” and through the results of 
certain spontaneous acts of the individual. 
* M. Vogt here refers to the recently discovered phenomena of “ alterna- 
tion of generations,” which may be briefly and popularly described as 
follows : — From a pair of individuals proceeds an offspring so different to the 
parents, that it appears to belong to a different order. These young ones are 
usually barren in the ordinary sense ; but by means of offsets, or some 
abnormal process, they produce a generation of individuals which are again 
fertile, and exactly resemble their “ grandparents,” if they may be so termed. 
