ZOOLOGICAL SOCIETY BULLETIN 



1583 



FIRE ROOM. NEW YORK AQUARIUM 

 Flooded at high tide. 



Photographed by L. L. Mo\ 



emergencies in the possession of a means for 

 manufacturing what might be called provisional 

 hands and arms. It is advisedly that we say 

 the mussel's foot is equal to the emergencies, 

 since its brains are under its foot and the foot 

 is therefore as good as a head. Indeed, rather 

 better than some heads. 



In the end of the foot is a byssogenous cavity 

 containing a byssus gland whose function it is 

 to secrete slender threads of conchiolin called 

 byssus threads which become hard and tough on 

 contact with the water. Each thread may be 

 likened to a long white arm with an open hand 

 at the end. The arm remains attached to the 

 base of the foot and can be broken off ; but the 

 hand, once fixed, adheres permanently to the 

 spot. 



When the animal wishes to change its posi- 

 tion, it puts out its foot and extrudes numerous 

 provisional hands and arms, or byssus threads, 

 which it attaches to the nearest objects upon 

 either side of it. as well as before and behind. 



drawing them taut as far ahead as it can reach, 

 in order that it may pull itself forward by means 

 of their support. The old threads are aban- 

 doned with each change of its moorings and the 

 threads in actual use may number seventy-five 

 or more. On glass, the sea mussel's tracks ap- 

 pear to the best advantage. 



The illustration shows the track of one as it 

 traveled up the glass in a tank of sea water, 

 searching, no doubt, for low water mark. It 

 spent some days in the ascent, but after climb- 

 ing eight inches, desisted and dropped to the 

 bottom, resuming the ascent a week later. Other, 

 smaller mussels in the same tank, climbed pa- 

 tiently till they reached the surface, which 

 necessitated a journey of nearly twelve inches, 

 and settled there. 



They all stop occasionally when traveling, 

 sometimes for several days at a time, perhaps 

 to rest or manufacture new byssus material, or 

 both. They have a preference for attachment 

 to shells. One young specimen fixed itself to 



