Alexander Onufrievich Kovalevsky (; 7 November 1840 – 1901) was a Russian embryologist, who studied medicine at the

University of Heidelberg Heidelberg University, officially the Ruprecht Karl University of Heidelberg (; ), is a public university, public research university in Heidelberg, Baden-Württemberg, Germany. Founded in 1386 on instruction of Pope Urban VI, Heidelberg is List ...

and became professor at the University of St Petersburg. He was the brother of the paleontologist Vladimir Kovalevsky, and the brother-in-law of the mathematician Sofya Kovalevskaya.

Discoveries

Comparison of Three Invertebrate Chordates

Kowalevsky's family belonged to Ukrainian nobility. He showed that all animals go through a period of

gastrulation Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals, the blastocyst, is reorganized into a two-layered or three-layered embryo known as ...

. Kovalevsky discovered that

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

s are not

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s, but that their larval stage has a

notochord The notochord is an elastic, rod-like structure found in chordates. In vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the intervertebral discs of the verteb ...

and pharyngeal slits, like

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s. Further, these structures develop from the same germ layers in the embryo as the equivalent structures in vertebrates, so he argued that the tunicates should be grouped with the vertebrates as

chordates A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...

. 19th-century zoology thus converted embryology into an evolutionary science, connecting

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

with homologies between the germ layers of embryos, foreshadowing

evolutionary developmental biology Evolutionary developmental biology, informally known as evo-devo, is a field of biological research that compares the developmental biology, developmental processes of different organisms to infer how developmental processes evolution, evolved. ...

Honors

He was elected on the 1st of May 1884 a Foreign Member of the

Linnean Society of London The Linnean Society of London is a learned society dedicated to the study and dissemination of information concerning natural history, evolution, and Taxonomy (biology), taxonomy. It possesses several important biological specimen, manuscript a ...

. The St. Petersburg Society of Naturalists annually awards the A.O. Kovalevsky Medal.

Bibliography

References

{{DEFAULTSORT:Kovalevskij, Alexander 1840 births 1901 deaths People from Preiļi Municipality People from Dvinsky Uyezd People from the Russian Empire of Polish descent Privy Councillor (Russian Empire) Biologists from the Russian Empire 19th-century zoologists from the Russian Empire Embryologists from the Russian Empire Full members of the Saint Petersburg Academy of Sciences Foreign members of the Royal Society Recipients of the Order of Saint Stanislaus (Russian), 1st class Recipients of the Pour le Mérite (civil class)