Simply stated, and thus less convincingly, it means that the embryos of all animals bother to provide a historical review of many stages of their evolution during their embryological development. Although this type of reminiscing is touching and is taught in almost every general science and biology text book, it is no longer accepted by scientists or even evolutionists. A tree that grows mainly in textbooks of biology and which has a variety of both contemporary and fossil animals perched on the tips of its branches. This tree clearly shows how all of these animals branched off from common ancestors a long time ago. For some reason the common ancestors are never shown sitting in the crotches of the tree.
Plants presumably grow on different trees which are rather rare.
Once known by all true scholars of human evolution to be an ancient ancestor of man. Today this ape-man is not so well known among true scholars of evolution. As the name implies, these are known to be the first true animals on earth. If these primitive organisms had continued to adapt to their changing environment they might still be with us today. An ad hoc hypothesis or alibi that claims the reason there are no known transitional forms in the fossil record is because evolutionary changes occur so quickly and the reason we can't see evolutionary changes in the laboratory is because they occur so slowly.