ADAPTATION FOR THE SPECIES 139 
against the trees until they are clean and smooth. 
Now he is ready for the battle royal. 
In the case of the fur seals polygamy has carried its 
specialization of the males to a remarkable extent. 
The bull seals are several times as large as the cows, 
and are provided with terrific canine teeth. With 
these they battle with a violence that very often re- 
sults in the death of one of the combatants. A suc- 
cessful bull seal who has gathered about him a clus- 
ter of seal cows is seamed and scarred with the marks 
of his annual combats. 
One more type of adaptation can be profitably con- 
sidered. Animals have developed many devices which 
serve for the protection of their young. The wonder- 
ful silk spun by the spider was evidently primarily in- 
tended to serve as a covering for the eggs. Probably 
all of our spiders agree in using the silk for this pur- 
pose. Many of them employ it for practically no 
other, though there are half a dozen different uses 
to which different spiders may put their silk. Under 
these conditions we have a right to infer that silk was 
primarily developed as a coating for the eggs. In 
the case of some of our spiders a little fluffy mass of 
silk covers the egg, while a firmly woven sheet of silk 
covers both egg mass and fluff, holding it flat against 
a wall or the trunk of a tree. In some of the higher 
spiders, notably our bank spiders, the silken covering 
