Page:Popular Science Monthly Volume 42.djvu/775

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STRUCTURE, ACTION, AND THOUGHT.

by the aid of an attempt at a skeleton—the so-called cuttlefish bone. But this has no joint in it, and even the octopus does not amount to much. Articulata with their jointed skeletons have reached such a pitch of social organization as to be held up for examples to mankind, and ants and bees are regarded by some as almost the mental equals, if not the superiors, of some of the savage tribes of mankind. But the outside skeleton is a sore disadvantage, for the animal must either remain without growing in

 
PSM V42 D775 Femur fibre arrangement for strength.jpg
Fig. 5.—Section of Head of Femur, to show the arrangement of the fibers of bone so as to give strength to it. (From Donald Macalister.)
 

size, or else it must be periodically cramped for room, and periodically burst its shell, leaving itself naked, weak, and defenseless. The right thing to do is evidently to do like the vertebrata, and have the hard parts inside, and the soft parts outside; but the relationship of these parts is a sore task upon the student's memory, and to many a one anatomy is a burden too heavy to be