240 BIOLOGICAL LECTURES. 



thrown into violent squirmings ; while the same stimulus applied 

 at the posterior end only hastens the normal progressive move- 

 ments. After a full study of the reactions of the earthworm 

 against injury, including also heat and electricity, it was found 

 that any stimulus having a definite local action would call forth 

 the two characteristic sets of reactions. 



Are there other animals whose reactions to injury are as 

 difficult to explain according to the pain-sensation theory as 

 those of the earthworm ? This question may be answered 

 positively in the affirmative. Let us consider the reactions 

 of animals chosen from four different groups. A live starfish, 

 as every one knows, may be cut into pieces with a pair of 

 scissors, or otherwise mutilated, without so much as calling 

 forth a responsive reflex action other than a temporary with- 

 drawal of the tube-feet. An arm thus cut off from the body 

 and left free in a little water soon begins to move about in 

 the same easy way that characterizes the motions of the whole 

 animal. 



The leech is perhaps the most highly differentiated of the 

 worms, and it is here that we should expect definite expression 

 of pain-sensations, if they are at all to be expected among such 

 forms of life. Yet what do we actually find ? The normal pro- 

 gressive movement of the leech in water is a rapid sinuous 

 swimming motion, carried out by the entire animal, but most 

 effectively by the flattened posterior portion. If now while 

 the animal is gliding through the water it be cut in two in 

 the middle with a sharp pair of scissors, both pieces without the 

 slightest reaction to the injury (or at most the slightest momen- 

 tary pause) continue to swim, with, however, a modified rate of 

 speed, due to their modified length and shape. 



The peculiar habit of crabs 1 of breaking off their thoracic 

 appendages near the base, due to strong stimulation, either 

 directly or indirectly, has been proved to be a purely reflex 

 action, and may take place even after removal of the brain. 



Among insects, the honey-bee has held an undisputed place 

 for intelligence by all who put the lower animals in the list of 



1 Fredericq, Leon, " Notivelles Recherches sur L'Autotomie chez le Crabe," 

 Archives de Biologic, XII, p. 169. 



