172 JULY. 



and behind the united fins. The conjoined fins do not 

 appear to me to make a vacuum. The fish has a curious 

 habit of coming to the surface of the water, and there 

 floating perfectly still, back downward, the entire belly- 

 surface dry. The ventral disk is then seen as a shallow 

 cup, quite dry and shining. If touched, the little fish 

 hurries along the surface, with some splashing, till it 

 acquires impetus enough to go under at an oblique 

 angle, when it presently turns over, and adheres to the 

 bottom, or side of some stone. I have seen this prac- 

 tice frequently, but only, I think, at night. 1 



This principle of a vacuum produced by the retraction 

 of the centre of a fleshy disk, while the margins remain 

 in close contact with a solid body, is of extensive appli- 

 cation in the lower forms of animal life, and especially in 

 the class ECHINODERMATA, comprising what are popularly 

 known as Star-fishes, Sea-urchins, and Sea- cucumbers. 



I have on other occasions noticed the elaborate and 

 wonderful mechanism of the sucker- feet as they appear 

 in the commoner species of the class. I need not there- 

 fore repeat those details, but look at a few other parti- 

 culars in the economy of the animals whose locomotion 

 is dependent on this curious contrivance. 



1 Let me refer my readers to an excellent and most interesting paper on 

 this little fish, by my friend, Mr. W. R. Hughes, in the Zoologist for 

 July 1864. 



