Embryology

The embryological development of an organism can tell us quite a bit about the evolutionary ancestry of the organism. For instance, as we saw in the exercise on Phyla Echinodermata, Hemichordata, and Chordata (Exercise 39), organisms can be classified as protostomes or deuterostomes depending on characteristics of early embryonic development.

Also, we can look to the types and locations of the germinal tissues to distinguish from one to the next. For instance, members of Phylum Cnidaria, discussed in Exercise 35, have only ectodermal and endodermal germ layers, so they are thought to be rather primitive. A distinguishing characteristic of members of Phylum Nematoda, discussed in Exercise 36, is that their coelomic cavity is only partly lined with mesoderm.

Today, genetics research has replaced much of the emphasis that was once placed on embryology. But, it is still a vital tool to determine the origin and development of organisms.