100 ANIMAL MECHANISM. 



It appears that the cephalic region lays hold on tlio fixcil 

 point touards which all the rest of the body is dragged for- 

 \\;inl. In fact, in the posterior region an opj)osite phenome- 

 non t.-ilccs place; each ue\v hand which takes its rise there, is 

 accompanied l.y a backward motion of that region, which moves 

 as if it were drawn by a longitudinal retraction of tlie con- 

 tractile tissue. 



Other modes of creeping are not less curious; that, for 

 example, which takes place in the interior of a solid body ; 

 na a worm, when it advances in the tubular cavity which it 

 has hollowed out in the ground. The hinder part of the body, 

 soft and extensible, is assuredly of much less size than the 

 cavity of the hole from which we endeavour to pull it, and 

 \rt the worm resists the force of traction, and breaks rather 

 iliati Le drawn out. This is because, within the ground, 

 the anterior portion of the body, shortened but swollen, dilates 

 within the passage, and finds there a solid point of resistance. 

 If we let the worm go we shall see it rapidly shorten its 

 body, and withdraw the rest, of it into the ground, being 

 dragged backward towards the anterior portion which has a, 

 firm hold on the soil. 



15y the side of the action of creeping we may naturally 

 place that of climbing, in which the anterior limbs seek to lay 

 bold of some elevated projection, and as they bend raise the 

 of the body of the animal. The hinder part then fixes 

 itself in its new posiiion, and the anterior limbs, thus set free, 

 seek, higher up, a fresh resting place to make a new effort. 

 What different types in these two modes of terrestrial locomo- 

 tion ! The varieties are so great that we can scarcely give 

 aa exact idea of them, except by describing the mode of pro- 

 gression adopted by each particular animal. 



/ i-oniiilion in unti'r presents a still greater diversity. In 

 -piie ease, \ve see a fish which strikes the water with the Hat 

 of its tail ; in another, a cuttle fish or a medusa, which, com- 

 pressing forcibly its pouch full of liquid, drives out the water 

 in one direction and propels itself in a course directly opposite ; 

 the same pin -non i en <>i i is pi odin-e-l wh -n a mollusk closes rapidly 

 the Valves of its shell, and projects it self in the direction opposed 

 to the cm rent of water which it lias produced. The larvie of 



