266 LAMARCK, HIS LIFE AND WORK 
to the reptiles, to the birds, even to the mammals, 
and you will see, except the lacuna which are still to 
be filled, everywhere shadings which take place be- 
tween allied species, even the genera, and where after 
the most industrious study we fail to establish good 
distinctions. Does not botany, which considers the 
other series, comprising the plants, offer us, in its 
different parts, a state of things perfectly similar? In 
short, what difficulties do not arise in the study and 
in the determination of species in the genera Lichena, 
Fucus, Carex, Poa, Piper, Euphorbia, Erica, Hiera- 
cium, Solanum, Geranium, Mimosa, etc., etc. ? 
‘““When these genera were established but a small 
number of species were known, and then it was easy 
to distinguish them; but at present almost all the 
gaps between them are filled, and our specific differ- 
ences are necessarily minute and very often insuff- 
cient. 
“From this state of things well established we see 
what are the causes which have given rise to them ; 
we see whether nature possesses the means for this, 
and if observation has been able to give us our ex- 
planation of it. 
“A great many facts teach us that gradually as 
the individuals of one of our species change their 
situation, climate, mode of life, or habits, they thus 
receive influences which gradually change the con- 
sistence and the proportions of their parts, their form, 
their faculties, even their organization; so that all of 
them participate eventually in the changes which they 
have undergone. 
“In the same climate, very different situations and 
exposures at first cause simple variations in the indi- 
viduals which are found exposed there; but, as time 
goes on, the continual differences of situation of in- 
dividuals of which I have spoken, which live and suc- 
cessively reproduce in the same circumstances, give 
rise among them to differences which are, in some 
