222 LAMARCK, HIS LIFE AND WORK 
as that of sensation: she has had the means of pro- 
ducing this faculty in the imperfect animals of the 
first classes of the animal kingdom,” referring to the 
Protozoa. But she has accomplished this gradually 
and successively. ‘“ Nature has progressively created 
the different special organs, also the faculties which 
animals enjoy.” 
He remarks that though it is indispensable to 
classify living forms, yet that our classifications are all 
artificial ; that species, genera, families, orders, and 
classes do not exist in nature—only the individuals 
really exist. In the third chapter he gives the old 
definition of species, that they are fixed and immu- 
table, and then speaks of the animal series, saying: 
“T do not mean by this to say that the existing 
animals form avery simple series, and especially evenly 
graduated; but I claim that they form a branched 
series,* irregularly graduated, and which has no dis- 
continuity in its parts, or which, at lcast, has not al- 
ways had, if it is true that, owing to the extinction of 
some species, there are some breaks. It follows that 
the species which terminates each branch of the gen- 
eral series is connected at least on one side with 
other species which intergrade with it” (p. 59). 
* Lamarck’s idea of the animal series was that of a branched one, 
as shown by his genealogical tree on p. 193, and he explains that the 
series begins at least by two special branches, these ending in branch- 
lets. He thus breaks entirely away from the old idea of a continuous 
ascending series of his predecessors Bonnet and others. Professor 
R. Hertwig therefore makes a decided mistake and does Lamarck a 
great injustice in his ‘‘ Zodlogy,” where he states: ‘* Lamarck, in 
agreement with the then prevailing conceptions, regarded the animal 
kingdom as a series grading from the lowest primitive animal up to 
man” (p. 26); and again, on the next page, he speaks of ** the theory 
of Geoffroy St.-Hilaire and Lamarck” as having in it ‘‘as a funda- 
mental error the doctrine of the serial arrangement of the animal 
world” (English Trans.). Hertwig is in error, and could never 
have carefully read what Lamarck did say, or have known that he 
was the first to throw aside the serial arrangement, and to sketch out 
a genealogical tree. 
