NATURAL HISTORY OF AMERICAN LOBSTER. 283 



Reflex amputation in crustaceans, whether considered in relation to shock or to fear, 

 or as an independent mechanism, must be regarded as one of the most remarkable 

 phenomena of invertebrate life. The loss of a considerable amount of tissue is always 

 a shock to a higher vertebrate, while a lobster in autotomy of both its cheUpeds may 

 give up with impunity one-half the weight, or even more, of its entire body. In the 

 higher animals fear may be due to inheritance or it may directly arise through asso- 

 ciation, by experience. The lobster, indeed, shows fear by hiding or by its hasty retreat 

 from an enemy, but reflex amputation does not appear to have any necessary relation 

 to fear. The reflex center of the cord is aroused to activity by a stimulus coming direct 

 through the nerves of the limb, and not from the brain. We may be sure that the 

 same center does not at one moment give the order to flee, and at the very next compel 

 the animal to drop any of its legs. The lobster or crab does itself a grievous injury 

 automatically in order to escape a worse fate. This kind of reflex surgery thus seems 

 to be an afterthought of nature, as if an attempt had been made to repair an earlier 

 mistake, or a compensation, as it were, for having originally endowed the crustacean 

 with a frame too vulnerable to attack, or with a mind too feeble to successfully cope 

 with its environment. 



RESTORATION OF LOST PARTS. 



The power of restoring lost or injured parts through the process of regeneration is 

 very general throughout the body and appendages of the lobster. It is exercised very 

 perfectly and promptly in the big chelipeds when thrown off by autotomy at the break- 

 ing plane, where the process has evidently been favored by natural selection or some 

 other factor of evolution. Regeneration is also very active in the fragile antennae and 

 the walking legs. All of these organs are, at the same time, very liable to injury, and 

 are essential to the maintenance of life by directing the animal to its food and enabling 

 it to secure it. In conveying this food to the mouth and preparing it for the stomach 

 the mandibles and other mouth parts are quite as important ; the swimmerets also serve 

 a variety of necessary functions, but all of these structures are far less liable to injury. 

 Whether there is a causal relation between liability to injury and facility to restore the 

 injured parts is another question. Morgan has reached a negative conclusion in his 

 experimental studies on the hermit crab, and concludes that "regeneration is a fimda- 

 mental attribute of Uving beings." The question, however, does not depend upon a 

 single relation; the relations are undoubtedly very complex, and it can not be denied 

 that in such animals as the lobster the external organs which are most exposed to injuries 

 of every kind and which are of immediate necessity for the maintenance of life possess 

 the most active power of regeneration. 



Emmel has shown {89) that the power of regeneration varies at different levels in 

 the limbs and that even the swimmerets may regenerate more rapidly than the legs if 

 the latter are cut off but a short distance below the breaking plane. Therefore the rate 

 of regeneration depends upon the place of injury as well as upon the amount of surplus 

 energy available at that point. 



The regeneration of a large cheliped in the fourth and fifth stages is essentially the 

 same as in the adult. At the moment the limb is broken off there is but little loss of 



