ISSN 10623604, Russian Journal of Developmental Biology, 2013, Vol. 44, No. 5, pp. 267–272. © Pleiades Publishing, Inc., 2013.
Original Russian Text © A.K. Dondua, R.P. Kostyuchenko, 2013, published in Ontogenez, 2013, Vol. 44, No. 5, pp. 357–363.
The selfsufficiency of the science about the devel
opment of an embryo, whose problems have been
drawing the attention of scientists since ancient times,
was apparently recognized in the 1840s after the pub
lication of the studies by K.M. Baer, which outlined
the range of issues faced by the researchers attempting
to understand the patterns of animal development.
The term “
” probably first appeared in the
scientific language in 1842, in the article by Karl Vogt
“Embryologie des salmons,” which was published in
Natural History of Freshwater Fish in Europe
edited by L. Agassiz (C. Vogt, 1842). By this time,
H. Pander and K. Baer had developed the doctrine of
the germ layers, which has become the cornerstone of
comparative embryology. It was found that, after the
completion of cleavage and blastula formation, spatially
separated cell areas,
, are formed in animals.
Karl Baer believed that germ layers are the universal
structures that appear in the early stages of embryogen
esis of all
Later, Alexander Kovalevskii
(1871) showed that the formation of germ layers is a
general characteristic of the embryonic development
of all multicellular animals, including invertebrates.
Germ layers homologous and universal for all
Eumetazoa were termed the ectoderm and the endo
derm. These terms were originally used to describe the
anatomy of adult Cnidaria (Allman, 1853). The cur
rently adopted nomenclature of germ layers—the
ectoderm, the endoderm, and the mesoderm—was
accepted in the embryological literature together with
the theory of Gastraea by E. Haeckel (1874), with the
help of Ray Lankester, an eminent British zoologist
(E. Ray Lankester, 1876 (cited by: Beetschen, 2001)).
An important step in the development of the doc
trine of germ layers was the establishment of the
ciple of specificity
, according to which each germ layer
of the embryo in different animals gives the same range
of derivatives. The outer layer, or the
, is the
source of epithelial and nervous tissue. The inner layer,
, yields the digestive system. The
threelayered animals, in addition to these two germ
layers, have one more, medium, layer, or the
, which yields muscles, connective tissue, blood,
coelomic epithelium as well as cartilage and bone skel
etons. The recognition of homology of germ layers in
all groups of animals has created a solid foundation for
comparative embryological studies. As emphasized by
our great compatriot P.G. Svetlov, without the theory
of germ layers comparative embryology “turns into a
chaos of facts” (Svetlov, 1963).
Today, the process of original morphogenetic trans
formation of the blastula, during which the germ layers
become spatially separated, is called
the Greek “
” (“stomach”)), because this pro
cess in the primitive forms is completed by the forma
tion of the archenteron, or the primary intestine. Gas
trulation takes place in all types of Metazoa except
sponges, whose tissue organization is very different
from the organization of Eumetazoa. Sponges do not
have the endoderm and never (neither in embryogen
esis nor after metamorphosis) form a gastric cavity.
Concerning One Obsolete Tradition:
Does Gastrulation in Sponges Exist?
A. K. Dondua and R. P. Kostyuchenko
St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia
Received February 26, 2013; in final form, April 4, 2013
—The analysis of comparativeembryological and molecularbiological data leads to the conclusion
that universal basic mechanisms of morphogenesis occurred first in the evolution of animals in the ancestors
of modern sponges and eumetazoans, which served as a basis of different evolution of individual development
in Parazoa and Eumetazoa lines. In the former, morphogenesis in early embryogenesis led to formation of the
watercurrent system as a means for capturing and delivery of food particles to different parts of the animal.
In the latter, morphogenetic movements manifested themselves as gastrulation, during which the germ layers
and the digestive system formed. The morphogenetic movements of cells in Metazoa emerged independently
of cell specification. They are primary relative to cell differentiation. The unity of all Metazoa is based on the
similarity of mechanisms of morphogenesis rather than on the presence of germ layers.
: gastrulation, germ layers, morphogenesis, evolution, Parazoa, Metazoa, sponges, cnidarians, Wnt
ONTOGENESIS AND EVOLUTION