Editing Embryology (section)

== Vertebrate and invertebrate embryology ==
Many principles of embryology apply to invertebrates as well as to vertebrates. Therefore, the study of invertebrate embryology has advanced the study of vertebrate embryology. However, there are many differences as well. For example, numerous invertebrate species release a [[larva]] before development is complete; at the end of the larval period, an animal for the first time comes to resemble an adult similar to its parent or parents. Although invertebrate embryology is similar in some ways for different invertebrate animals, there are also countless variations. For instance, while spiders proceed directly from egg to adult form, many insects develop through at least one larval stage.
For decades, a number of so-called normal staging tables were produced for the embryology of particular species, mainly focussing on external developmental characters. As variation in developmental progress makes comparison among species difficult, a character-based [[Standard Event System]] was developed, which documents these differences and allows for phylogenetic comparisons among species.<ref>{{cite journal |last1=Werneburg |first1=Ingmar |title=A Standard System to Study Vertebrate Embryos |journal=PLOS ONE |date=2009 |volume=4 |issue=6 |pages=e5887 |doi=10.1371/journal.pone.0005887|pmid=19521537 |pmc=2693928 |bibcode=2009PLoSO...4.5887W |doi-access=free }}</ref>