288 BIOLOGICAL LECTURES. 



will hug the glass with its body somewhat expanded. Now 

 push the needle slowly along towards the leech, and notice, as 

 the needle comes almost in contact with the thin margin of the 

 body, that the part nearest the needle begins to retreat slowly 

 before it. This behavior shows a surprising keenness of tactile 

 sensibility, the least touch of the water with a needle-point 

 being felt at once. This delicate sensitiveness is manifested 

 in such a quiet way that it would be generally overlooked, and 

 an observer unfamiliar with the habits of Clepsine, and not 

 realizing the necessity of extreme quiet in his own movements, 

 would almost certainly draw false conclusions. If the dish 

 were moved or the water carelessly disturbed in any way, the 

 Clepsine would assume its motionless attitude and appear to be 

 wholly indifferent to the disturbance. If its back were rubbed 

 with a brush or the handle of a dissecting needle, in order 

 to test its sensitiveness to touch, the appearance would prob- 

 ably still be that of insensibility and indifference to the treat- 

 ment. Closer examination, however, would show that the flesh 

 of the animal was more rigid than usual, and that the surface 

 was covered with numerous small, stiff, conical elevations, the 

 dermal papillae or warts, which are so low and blunt in the 

 normal state of rest as to be scarcely visible. It would be 

 seen that the animal, although motionless, was in a state of 

 active resistance to attack. Every muscle would be strained ; 

 the whole skin would be tense and rough with the stiff, pointed 

 papillae ; and at the same time the body would be found exces- 

 sively slippery and difficult to lay hold of, owing to the mucous 

 secretion poured forth from the dermal glands. To guard still 

 further against dislodgment, the body would be flattened out as 

 much as possible and tightly applied to the glass. The activity 

 of the resistance offered by this passive-looking creature would 

 be very forcibly realized if the observer attempted to circum- 

 vent it by slipping a thin blade or spatula beneath it with a 

 view to forcing its hold. If overcome in one part it would 

 stick by another, and skillful manipulation would be necessary 

 to get both ends free at the same time. With one end detached, 

 the other will often hold against a pull strong enough to snap 

 the body in two. 



