260 EVENINGS AT THE MICROSCOPE. 



"will take the trouble to thrust a spade into the ground, and 

 give it two or three shakes. You will presently see on all 

 sides the alarmed Earth-worms coming swiftly to the 

 surface, and will notice how perfectly sleek and clean 

 they are. 



But these contrivances are only accessories : we have 

 not yet discovered the secret of the easy movement. The 

 mere elongation of the snout is no explanation of the dis- 

 appearance of the "Worm in the burrow ; for you will 

 naturally and reasonably say that this elongation cannot 

 extend beyond a certain limit ; and what then ? No fur- 

 ther progress can be made unless the hinder parts of the 

 body are, by contraction, drawn up towards the elongated 

 front ; — but what holds the front in place meanwhile ? Why, 

 when the muscles contract, does not the taper, wedge- 

 like muzzle slip back and lose the ground it had gained ? 



This we will now look at. I take up this Worm, and 

 put it into a narrow glass cell, where we may watch its 

 movements. It presently begins to elongate and contract 

 its body vigorously, apparently alarmed at its unwonted 

 position ; and the mucus is thrown off in copious abund- 

 ance. We apply a low microscopic power to it, and catch 

 glimpses, now and again, as it writhes about, of a number 

 of tiny points protruded and retracted with great regularity 

 through the skin. Its mobility precludes our discerning 

 much more than that these points are very numerous, that 

 they are arranged in four longitudinal lines, running along 

 the ventral side of the animal, — two lines on each side, — 

 and that in each line there is a point protruded from each 

 of the many rings of which the Worm's body is made up. 



In order to see a little more of these organs we must 

 sacrifice a Worm ; having killed it, and divided the body 

 in the middle, I cut off, with sharp scissors, a small trans- 

 verse portion, say two or three rings, and press the 

 fragment between plates of glass. Now, with a higher 

 magnifying power, we discern in the midst of the trans- 



