42 EVENINGS AT THE MICROSCOPE 



of comparison, we find, on applying the micrometer, that 

 the disks run from l-2500th to l-5000th of an inch; but 

 that the great majority are about 1 -3300th in diameter. On 

 these slides are samples of other kinds. This is the blood 

 of a Fish the common Blenny or Shanny (Blennius pholis). 

 Here we see at once the oval form of the disks ; their aver- 

 age is l-2800th by l-SSOOth of an inch. Here is the blood 

 of a Frog (Rana temporaries)] these are more than twice 

 the size of the fish's; for they average l-1250th by 14800th 



BLOOD-DISKS. 



a, Man. 6, Blenny. c, Frog. d, Newt. 



of an inch. And, finally, I can show you a drop of blood 

 from this Smooth-newt (Lissotriton punctatus). The large 

 size of the disks is now conspicuous, and so indeed is the 

 elegance of their form: in this case, as in the last, we see 

 in each disk a distinct roundish nucleus. These run from 

 1 -700th to l-950th in length, by 1-llOOth to l-1600th in 

 breadth; but the average are about 1 -800th. by l-1300th 

 of an inch. 



It may interest you to see these blood-disks in their 

 proper situation, and to observe the motion which they 

 possess during the life of their owners. It is, indeed, one 

 of the most instructive modes of using this wonder-work- 



