396 
CEUAE TE Recline 
THE CETACEA. 
IN animals of a simple construction the tissue of their substance 
is homogeneous, all their organs being composed of the same kind 
of matter; the functions of these organs, moreover, are reduced to 
the lowest limit, their exercise being expended upon that only 
which is absolutely necessary to existence. As we ascend the 
scale, we find that the functions of the various organs become more 
definite or localised, that is, one organ only performs a special 
office, and does not undertake several functions. 
The division of labour in the body, among the various organs, 
is one of the most curious and intcresting of the laws of Nature, 
and the higher the position occupied by an animal in the scale of 
creation the more organs it possesses. Just as in the humbler 
position of our society the work of the household is done by a 
“maid of all work,’ and as a higher grade is reached, more 
numerous become the domestics, the several duties of an establish- 
ment being allotted, each to a separate servant; and thus the 
number of retainers is a good measure of the position of the 
householder. 
In the higher orders of life—in those animals which approach 
the master-piece of creation, man—the various functions of the 
body are performed by organs which are either single or double. 
The brain and heart, the essential organs of vertebrate life, are 
single, while the organs of vision and hearing are double. 
In the annelids all the organs are repeated an incredible num- 
ber of times. Some species have ten jaws, some 300 claws, and 
in some the eyes are legion, even reaching 30,000. 
As we saw in Chapter XXIX., the Zoonites are composed of an 
assemblage of organs, so arranged that the animal is built up of 
segments, each segment having a complement of organs; and yet 
the zoonite is far below the vertebrates in the scale of life ; a single 
