Please define "acquired" in this context. 
The usual simplistic example is that because the proto-giraffe's mother "wanted" to reach higher her baby had a longer beck. Whereas, of vourse, those proto-giraffes born with slightly longer necks out-competed the short-necks.
Goats selected for tree climbers.
Again, I'm not defending Lamarck's theory or his specific examples such as a giraffe's neck. But here is a summary of his theory from Wiki: "In essence,
a change in the environment brings about change in "needs" (besoins), resulting in change in behavior, bringing change in organ usage and development, bringing change in form over time—and thus the gradual transmutation of the species." (emphasis added).
Now, from xSilverPhinx's article: "But the environment we live in can make genetic changes, too. Researchers have now discovered that
these kinds of environmental genetic changes can be passed down for a whopping 14 generations in an animal – the largest span ever observed in a creature, in this case being a dynasty of C. elegans nematodes (roundworms)."
See the similarity? Obviously Lamarck knew nothing of genetics or DNA, so he had no idea how these changes occurred. But, again, his general thesis was not that far off.