Beginning around the turn of the 20th century, embryologists started to realize the potential of experimental approaches to investigating development. By intervening in normal development—shaking embryos, splitting them apart, soaking them in various solutions, transplanting pieces of one onto another, and so on—researchers discovered aspects of embryogenesis that they were unable to see with purely descriptive studies. The success of these experimental approaches depended on visual media to document experimental outcomes and describe exactly how experiments were done. Johannes Holtfreter and Viktor Hamburger were highly skilled experimentalists who established many of the techniques and tools that are still used to manipulate embryos. Many of the pioneering experiments they did with amphibian and chick embryos, respectively, laid the foundation modern day research in these organisms.