354 APPENDIX. 



more properly a sucker ; the other probably has 

 other functions, since he could never ascertain 

 that it was used for prehension. 



A kind of metamorphosis seems to take place 

 in these animals, for our author observed that 

 they appeared under three different forms. 



These little pests, small as they are, have a 

 parasite of their own to avenge the cause of the 

 perch, for Dr. Nordmann observed some very 

 minute brown dots or capsules attached to the 

 intestinal canal, which when extracted, by means 

 of a scalpel formed of the thorns of the creeping 

 cereus, 1 and laid upon a piece of talc, the mem- 

 brane that inclosed them burst, and forth issued 

 living animalcules, belonging to the genus Monas, 

 and smaller than M. Atomus, which immediately 

 turned round upon their own axis with great 

 velocity, and then jumped a certain distance in 

 a straight line, when they again revolved, and 

 again took a second leap. 



Looking over our author's list of eye-worms 

 that infest fishes, we find that five out of seven 

 are attached to different species of perch, and 

 one cannot help feeling some commiseration for 

 these poor animals ; but when we recollect that 

 they form the most numerous body of preda- 

 ceous fishes in our rivers, we may conjecture that 

 thus their organs of vision are rendered less 

 acute, and that thus thousands of roach, dace, 



1 Cactus flagelliformis, 



