Circulation of the Blood. 143 



with a fish or tadpole. It is to be placed in a little 

 bag, and this is to be tied on the brass " frog-plate/' 

 sometimes supplied with a microscope, or on the 

 wooden imitation of it, which can be very easily cut 

 out with a penknife. The shape is shown at No. 24, 

 g, and the bag may be also seen, containing the frog 

 with one foot left out, the claws of which are fastened 

 by bits of thread to some little wooden pegs. The 

 frog-plate must have two other pegs on the under 

 side to fasten it to the holes generally to be found in 

 the microscope's stage ; it should also have a square 

 hole over which the frog's foot is to be extended, and 

 I found it convenient that it should have some fixed 

 strings attached to it. The great point is not to give 

 the frog room to draw in its foot, and the pair of 

 strings tied in front of its head generally insure 

 this. 



The circulation in small water-newts, and various 

 water larvae and crustaceans, may be easily shown by 

 placing them in the live-box with a drop of water. 

 No. 25 represents a small and singular crustacean, 

 called Daplmia pulex. The remarkable branching 

 appendages over its head are anfcnnce, or feelers ; and 

 it has but one eye, consisting of several lenses en- 

 veloped in a single cornea, which encloses them all. 

 The whole of the circulation may be seen, though in 

 a vague and rudimentary manner, in this little crus- 

 tacean. There is a rapidly beating heart near its 

 back, and from this colourless particles may be seen 

 flowing and performing a circuit of the whole frame. 

 Daphnia breathes not exactly by gills, " but by means 



