“A CHIP FHOM MANY OLD BLOCKS.” 231 
are always unequal in size. We have here, then, 
a simple case of cell fertilization and a suggestion 
of sex. 
Higher animals, as is well known, are composed 
of many cells united into one being. The cells also 
become differentiated—that is, each set has its own 
function to perform. There are muscle-cells, bone- 
cells, nerve-cells, reproductive-cells, and so on. They 
are divided into two groups : the reproductive or 
germ-cells, and the body-cells. The germ-cells alone 
have the so-called hereditary ‘‘threads.” The off¬ 
spring gets both germ-cells and body-cells from the 
parent, and it is with the germ-cells that the heredi¬ 
tary threads are transmitted. These threads have 
the power of directing the growth of the body- 
cells, and thus construct a body which possesses the 
traits of the parent. What power in the cell accom¬ 
plishes this work is not known, but we may sum it all 
up in the word life. 
“A CHIP FROM MANY OLD BLOCKS.” 
Life everywhere presents two important facts. 
The one has already been explained under heredity; 
the other is variation. Heredity gives us types which 
may be recognized even in the midst of much modifi¬ 
cation. Variation gives Us new species and new 
varieties. 
There are many things which act upon life so as 
to produce variation. Earth, air, water, food, and 
exercise, each has its significant infiuence upon life. 
