THE PRINCIPLES OF BIOLOGY. 
309 
Stem short and thickisli; swelling ovoid; basal reservoir 
roundish, usually above the matrix; spores yellow, spherical, 
rather unequal, 105-14*8/*, with a distinct, thick, bluish 
epi spore. 
On horse, cow, goat, and pig dung, and on mud, algse, and other 
decaying substances. It seems to be the commonest form on human 
excrement. Spores germinating easily in water; columella conical, 
obtuse, sometimes piercing the sporange almost to the summit. 
Not common. (Figs. 14, 15.) 
England, France, Belgium, Germany, America. 
2.—PILOBOLTJS EXIGTJUS, Bainier. 
r. exignus, Bainier, “Etude,” p. 47, pi. 2, f. 17 (1882). 
Stem rather thick and short; sporange round, black but 
transparent; spores spherical, yellow, unequal, 14*7-21^; 
swelling scarcely developed; basal reservoir concealed 
roundish. 
A small and doubtful species, possibly a form of P. cedipus. 
France. 
THE PRINCIPLES OF BIOLOGY. 
BY HERBERT SPENCER, 
EXPOSITION OF CHAPTER V.-ADAPTATION. 
BY WILLIAM L. HIE PE. 
Adaptation in its wider sense may be defined as the 
power of species of animals or plants to vary under altered 
circumstances, so as to become again harmonised with the 
environment. In fact, in the power of adaptation we have 
one of the agencies by which new species are produced. But 
adaptation of a whole species can only be brought about by 
adaptation of single individuals during many generations, and 
it is this adaptation of single individuals or their parts to 
altered circumstances with which Chapter V. treats principally. 
In speaking of a single individual adaptation may be described 
as the power by which in each part of the body the supply of 
nutritive matter is regulated according to the requirement, 
and it is, therefore, a necessary concomitant of function. An 
organism without the power of adaptation would resemble a 
steam engine which drives several machines, but has no 
appliances by which to regulate the supply of force to each 
machine according to the work required to be done by it. 
