CHAPTER IX 
CONDITIONS OF EXISTENCE OF LAND ANIMALS 
I. INTRODUCTION 
Man being a land animal, it is natural that he should be more familiar 
with the conditions of existence of land animals than with those of aquatic 
forms. The reader will recognize that the primary divisions into which 
land animals may be divided are (a) those living exposed to the atmos- 
phere on the surface of the soil and of plants and animals, and (0) those 
out of direct contact with the atmosphere, in the soil, in wood, and in the 
tissues of living plants and animals. The solid substances in and upon 
which animals live are called materials for abode (55, 115) and, aside from 
soil, materials are just as varied as are the living and decaying bodies of 
plants and animals. For this reason, an adequate discussion of such 
materials for abode would require a separate treatise. Since the laws 
governing the physical conditions surrounding animals living hidden 
away, for example in the bodies of living and dead organisms, are little 
known, we will pass directly to a discussion of the conditions of existence 
of animals living in soil and exposed to atmosphere. 
fT.) SOLE: Ger) 
Because of its importance in agriculture, the relation of plants to soils 
has been much studied. The laws governing plants in their relation 
to soils apply in the main to soil-inhabiting animals, all the various 
properties of soils being of some importance in this connection. 
I. TEXTURE 
The texture of soils is of importance to animals because of the vary- 
ing difficulty with which they may burrow into it, and the ease with 
which their burrows are maintained when once dug. Particular animals 
prefer soils of a particular texture, some preferring rock, some sand, etc. 
2. WATER 
Most subterranean animals are submerged in water during rains. 
The amount of water which they encounter in the soil at other times is 
determined to a large extent by their relation to the water table (57), and 
by the character of the soil. The water-holding power of different soils 
is different. It increases with the decrease in size of the soil particles and 
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