DEVELOPMENT. 
215 
continually growing; the long bones of higher animals 
increase in length so long as the ends (epiphyses) are sep¬ 
arate from the shaft. The limbs of Man, after birth, 
grow more rapidly than the trunk. 
The power of regenerating lost parts is greatest where 
the organization is lowest, and while the animal is in the 
young or larval state. It is really a process of budding. 
The upper part of the Hydra, if separated, will reproduce 
the rest of the body; if the lower part is cut off, it will 
add the rest. Certain Worms may be cut into several 
pieces, and each part will regain what is needed to com¬ 
plete the mangled organism. The Star-fish can reproduce 
its arms; the Holothurian, its stomach ; the Snail, its ten¬ 
tacles; the Lobster, its claws; the Spider, its legs; the 
Fish, its fins; and the Lizard, its tail. Nature makes no 
mistake by putting on a leg where a tail belongs, or join¬ 
ing an immature limb to an adult animal. 120 In Birds and 
Mammals, the power is limited to the reproduction of cer¬ 
tain tissues, as shown in the healing of wounds. Very 
rarely an entire human bone, removed by disease or sur¬ 
gery, has been restored. The nails and hair continue to 
grow in extreme old age. 
4. Likeness and Variation. 
It is a great law of reproduction that all animals tend 
to resemble their parents. A member of one class never 
produces a member of another class. The likeness is very 
accurate as to general structure and form. But it does 
not descend to every individual feature and trait. In 
other words, the tendency to repetition is qualified by a 
tendency to variation. Like produces like, but not ex¬ 
actly. The similarity never amounts to identity. So that 
we have two opposing tendencies — the hereditary ten¬ 
dency to copy the original stock, and a distinct tendency 
to deviate from it. 
