358 APPENDIX. 



times one appears inclined to move to the right, 

 and the other to the left, or one to move and the 

 other to remain at rest ; but the lower lobes 

 always move simultaneously, either inwardly or 

 outwardly. 



The animals that are found attached to the gills 

 of other fishes are usually at their lower extremity 

 furnished with several suckers ; thus one genus 1 

 infesting the gills of the sun* and sword fishes 3 

 has three ; and another, 4 found in those of the 

 tunny, 5 has six, whence Cuvier would rather 

 call it Hexastoma. But these are nothing to 

 those of our Diplozoon, which, on the four disks 

 just named, has no less than sixteen suckers, four 

 on each disk. 6 Under a strong magnifier, these 

 suckers when opened, for they can open and 

 shut, exhibit a complex machinery of hooks and 

 other parts, by which their Creator has enabled 

 them to take firm hold of the gills, so as not to 

 be unfixed by their constant motion in respira- 

 tion, especially when we consider their structure 

 and substance. A further proof of this design is 

 furnished by the form of the animal itself, for 

 the body being divided upwards and downwards 

 into two diverging lobes, it can fix itself at each 



1 Tristoma. 2 Mold. 3 Xiphias. 



4 Polystoma. 5 Scomber Thynnus. 



6 Even this is nothing to those of a genus infesting some 

 Cephalopods, Hectocotyle,t\ie different species of which have from 

 sixty to more than one hundred suckers, whence their name. 



