128 CELL THEORIES. 
of the specially developed properties. In muscular 
fibre it appears to be lost altogether. ] 
Probably the greatest difficulty in conceiving 
of the origin of differentiated textural elements 
from common corpuscles is to settle the relation of 
epithelial to other corpuscles, and on that subject 
it is not easy to give an opinion. In particular, 
the phenomena of skin-grafting, including the 
stimulus given to the growth of skin over a whole 
ulcer by the presence of grafts of minute size, 
might even suggest the possibility of a sexual 
distinction between the corpuscles of the graft and 
those among which it is planted. At all events, 
the microscopy of skin-grafting is worthy of study, 
and the utility of the practice affords evidence that 
all the less differentiated corpuscles are not capable 
of producing, at least without assistance, all other 
kinds of corpuscles. [Evidence of this is especially 
to be seen in the circumstance that the most 
effective grafts are those which completely dis- 
appear before being succeeded by a transparent 
pellicle which spreads ; and also in the well-ob- 
served fact that improvement in an ulcer to which 
grafts have been successfully applied is not con- 
fined to the spots where they have been placed.] 
It must be kept in mind that the corpuscular 
mass of the embryo becomes early divided into 
