On the resistance of Fluids. 359 



It is not impossible that these animals feed also on animalculae, if 

 unable to obtain what may be a more delicious morsel to them, the 

 body of the clam. Indeed this is quite probable, as we have kept 

 several of them nearly two months, in a cup of water, and they still 

 retain all their usual activity, and appear really to have fattened on 

 the animalculae which the stagnated water has afforded them. In 

 this state of confinement, they show no disposition to molest one an- 

 other, but are continually occupied in walking, with occasional at- 

 tempts to swim, along the bottom and sides of the cup. In walking 

 they rely principally on their second and third pair of legs, occa- 

 sionally using however, the others. 



Explanation of the plate. 



Pig. 1. Back view of female, a, palpi. From b to the extremity of the inner 

 abdomen, appear lines which represent the vessels connected with the stigmata be- 

 low, (fig. 2, c, c.) 



Fig. 2. Under view of the same, c, c, stigmata. 



Fig. 3. Under view of the palpi, e, e, two prominences forming the bifid lin- 

 guette of authors. /, sucker, situated nearly at right angles with the body. 



Fig. 4. Profile view of the sucker. 



Fig. 5. The same protruded. 



Fig. 6. Side view of the palpi. 



Fig. 7. Tarsus of a posterior leg, exhibiting the hooks which terminate the same 

 joint of each pair of legs. 



Fig. 8. Length of female and male. 



Fig. 9. Outline of the body of H. pyriformis. 



Art. XI. — On the Resistance of Fluids, in reply to Professor 

 Keely, ivith remarks on the measure of Mechanical Power ; 

 by Eli W. Blake. 



TO PROFESSOR SILLIMAN. 



Prof. Keely, in the last number of the Journal of Science, 

 has amused your readers with some strictures on my communication 

 to the preceding number, on the resistance of fluids. His argu- 

 ments in these strictures are founded, so far as they have any foun- 

 dation, on a misapprehension of my meaning. I solicit therefore 

 the favor of a page or two in your ensuing number to correct this 

 misapprehension, and to urge still further the general views which it 

 was my principal object in that communication to express. 



In penning the article referred to, it was far from my wishes to 

 array myself in opposition to the views of any individual, for I had 



