16 WILLIAM PATTEN. 



below are chitinous is shown by their resistance to caustic 

 potash, and by the fact that they are shed during ecdysis. On 

 examining cast-off shells one can see the perfectly preserved 

 tubule projecting out of the inner ends of the cuticular canals. 

 Each spine on the jaws is crowded with the organs just 

 described, and contains also a large blood-vessel. There can 

 be no doubt that they are the gustatory organs, which, when 

 stimulated, produce the reflex chewing movements described 

 above. 



c. Experiments on the Gustatory and the Tem- 

 perature Organs of the Chelae. — Two varieties 

 of organs, having nearly the same histological 

 structure and arrangement as those on the mandi- 

 bular spines, are found on the last two joints, or 

 chelse, of the first to sixth appendage. One kind 

 is a gustatory, the other, in all probability, a tempe- 

 rature organ. 



The presence of the gustatory organs may be demonstrated 

 by the following experiments : — Place a crab on its back and 

 allow it to become quiet ; then if the chelse, which are 

 usually lightly closed, are rubbed with a small piece of clam, 

 they will open wide, and remaining so, move about rather 

 vaguely, as though trying to grasp something. They are 

 specially sensitive at the tips and along the cutting edge. 

 Ammonia vapour will produce the same result, but it cannot 

 be produced by any purely mechanical stimulus. 



The temperature organs betray their presence by an entirely 

 different action, for if one breathes very gently, or blows warm 

 air on the chelae, they suddenly close and open once, and will 

 repeat the action without variation as often as they are 

 stimulated in this way. 



A very curious fact is the following : — If the chelae are 

 amputated at the penultimate joint, they remain perfectly 

 quiet if left alone. But for five or ten minutes after the 

 operation they will snap once, i.e. close and immedi- 

 ately open again, every time they are gently 



