THE AMERICAN LOBSTER. 129 



nent nucleus at the peripheral end of this cell, there are two other bodies — one near the 

 tubular neck — which take up the stain like nuclei and are considerably refractive. 

 From the larger end of the cell (tig. 206) a slender process is given off (compare figs. 

 201,204 from the maxillae), which suggests a nerve fiber. All that I can say definitely 

 is that this process is in continuity with the cell, probably with its wall. I did not see 

 many cases of a similar character. 



EXPERIMENTS UPON THE SENSORY AREAS OF THE BODY AND APPENDAGES. 



Before discussing the function of the tegumental organs in general, I will record 

 some experiments which were made to determine how the lobster reacts to stimuli 

 directed against the dead shell or cuticle. 



The lobsters experimented upon were taken from the sea, placed on their backs 

 on a table, and allowed to remain in this position until quiet. At first they move 

 their appendages vigorously in trying to right themselves, but soon come to rest. By 

 sprinkling them with sea water they may be kept fresh for experiment for a consider- 

 able time. 



Various stimuli, such as electricity, heat, weak acetic acid, ammonia gas, clam juice, 

 were applied to different parts of the body, with a view to ascertain the most sensi- 

 tive areas where the quickest and most vigorous responses were given. 



The degree of sensibility to external stimuli is surprisingly great in many cases, 

 where the skin of the lobster with its shelly covering seems quite as sensitive as that 

 of the frog. In other cases, however, the animal is much less responsive, a fact which 

 we may attribute in some degree to the thickness of the shell. 



To sum up the experiments in a general way, all or nearly all the appendages 

 react strongly to chemical stimuli, and in many cases the surface of the body is 

 capable of receiving and responding to stimuli of various kinds. If a jet of ammonia 

 gas is injected against the intersegmental membranes or appendages of the ''tail," the 

 pleopods may be set in very lively motion and violent flexion of the whole abdomen 

 may follow. Direct the jet upon the anterior swimmerets, and the last three pairs of 

 walking legs are drawn backward and make scratching movements to remove the 

 offending object, reminding one of the motions of a "reflex frog" when its skin is 

 stimulated in a similar way. 



The reaction is more violent when the stimulus is applied to the swimmerets than 

 when directed against the intersternal membranes. The seminal receptacle is very 

 sensitive, and when stimulated the walking legs make violent scratching movements 

 toward it. If the jet of gas is directed along the surface of the walking legs, the 

 reaction is usually greatest at their tips. 



If the extremities of the large chelae, especially the propodus, are touched by the 

 gas the claw opens and shuts. The first pair of antennae are much more sensitive to 

 the stimuli than the second pair. If the jet is directed over the region of the mouth, 

 very violent chewing movements are set up. 



If the ammonium vapors be squirted on the dorsal surface of the carapace or 

 abdomen, a vigorous response is sometimes seen by the immediate movements of the 

 legs. Both males and females respond to the ammonia stimulus on the abdominal 

 appendages and intersegmental membranes. 



Very similar reactions are obtained if a small piece of blotting paper wet with 

 weak acetic acid is used. In some cases no response is obtained if the wet paper is 



F. C. B. 1895—9 



