living Pyrensematous Vertebrates. By W. II. Hammond. 149 
appearance to what it has when seen in the corpuscles after they 
have been drawn from the body and put on a glass slide. 
In conclusion, I think I have now proved the existence of a 
nucleus in the living red blood-corpuscles of fishes, batrachians, 
and birds. I have been as careful as possible when making my 
observations to guard against errors, and when making the obser- 
vations under the high power, I sat a whole day watching the 
circulation in the tadpole of the frog and newt. 
I must add that though the nucleus can he seen in fishes very 
plainly under a half-inch objective, with ordinary illumination, yet 
in frogs, newts, and tadpoles, it requires a much higher power, and 
even then, unless the light is carefully regulated, the nucleus may 
be missed. I used a Webster condenser with the iris diaphragm, 
and found that as much care was required with the illumination as 
when resolving difficult diatoms. 
August 2 , 1877 . 
