The science of life : fully illustrated in tone and line and including many diagrams

THE SECOND GREAT PHYLUM: THE ARTHROPODS

of the pocket workshop variety animated with a will of its own.

On opening the lobster and examining the organs that lie within his hard exterior we find other striking contrasts with ourselves. The armour, we find, is the lobster’s skeleton; he has no bones that correspond to ours, and except in a few places where rods project

Heart

salts, and it is secreted by a layer of cells that lies immediately below it.

Since the lobster lives inside his own skeleton, the mechanical arrangements of his limbs and other movable parts have to be different from

Gonad Stomach

Intestine Fig. 78.

Nervous System

The body of the Lobster of Fig. 79, cut lengthways to show where

some of the more important organs are placed. The so-called liver, which fills the front half of the body, is left out of the drawing for

clearness.

from the surface into the soft interior in order to give firm attachment to the muscles of his limbs, and except for a marvellous chewing apparatus in his stomach, this outer coating is the only rigid tissue he possesses. Like the hard substance of our own skeletons it is made by but not of living cells; it is dead matter consisting largely of a horny substance called chitin, and strengthened by the deposition in it of lime

Fig. 79.

ours. Inourselves, the jointed bones are clothed by a layer of muscles which pulls them in various directions ; in the lobster, instead of bones there are jointed tubes, and the muscles that move them lie inside them.

‘The lobster’s main interior cavity in the cephalothorax

The Common Lobster (Homarus vulgaris) (From the Plymouth Aquarium Guide, by courtesy of the Marine Biological Association af the United Kingdom.)

Fig. 80. A Lobster’s jointed limb opened up to show the muscles lying inside. Contrast these mechanical arrangements with those

of the human arm in Fig. 6.

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