No linking :

It is no doubt difficult even to conjecture by what gradations many structures have been perfected ...
... although in many cases it is most difficult even to conjecture by what transitions organs have arrived at their present state ...
CHARLES DARWIN , Origin of Species . Chapter V1 , Difficulties with theory N

“... the distinctions of specific forms and their not being blended together by innumerable transitional links, is a very obvious difficulty.” Charles Darwin, The Origin of Species, 6th edition (New York: Macmillan Publishing Co., 1927), p. 322.