METHODS OF PROTECTION AMONG ANIMALS. 149 
lightness, strength, and beauty. The skeletons of the great 
group of corals may also illustrate these primary and 
secondary purposes in the building up of great islands and 
continents. Sea anemones have no hardened exoskeleton, 
but they possess an external layer of hardened tissue 
containing the substance “chitin” just mentioned. 
The Echinodermata, or sea-urchins, starfishes, and sea- 
lilies, present a very hard and varied coat fashioned by the 
animal from the ingredients of the sea-water in which the 
animal lives, It is enough to mention these familiar forms 
of protective structure without further description, except to 
refer to the movable spines often found on the plates of the 
shell or coat, some of which are capable of bestowing 
painful wounds on enemies by means of a stinging apparatus. 
Altogether this group of sea-urchins, starfishes, and the like 
are well able to take care of themselves, which fact may 
account for their great antiquity as a family, dating from 
Palaeozoic times. 
The great group cf Annulosa comprises worms, of various 
forms, speders, crabs, lobsters, shrimps, and insects of all 
kinds. 
In worms there are no such spicules forming a skeleton 
as in the sponges, nor any complete endoskeleton. But 
protection is given by an outer tough coating in some; in 
others the same with muscles attached to it. In sedentary 
annelids inhabiting the sea there is a protecting tube, 
sometimes further hardened by the deposition of calcareous 
salts, sand, mud, or other foreign substances. In some a lid 
is provided at the entrance to this tube, capable of closing 
the aperture. In certain chatopod worms some gland- cells 
of the outer skin secrete hard bristles, serviceable for 
protection. The earth-worm has also an abundant slimy 
secretion on the surface, serving efficiently to protect it. 
The great group of insects ‘consists of animals with the 
body divided into head, thorax, and abdomen, each of these 
parts being protected by contrivances of various kinds, 
The antenne and jaws borne by the head contribute to 
the protection of the possessor, and the simplest well-known 
example of protection in the case of the jaws is that of the 
mandibles of the stag-bettle, resembling horns in shape. 
The head is also strongly protected by a ‘chitinous covering, 
as is also the thorax, that of the abdomen being of a softer 
and more mobile character. 
In addition to the dense tough covering of an insect such 
