On this date, the Russian founder of comparative embryology and experimental histology Aleksandr Onufriyevich Kovalevsky was born. He was the first to establish that there was a common pattern in the embryological development of all multicellular animals.
Kovalevsky began by studying the lancelet, a fish-shaped sea animal about 2-in. (5-cm) long; he then wrote Development of Amphioxus lanceolatus (1865). In 1866, he demonstrated the similarity between Amphioxus and the larval stages of tunicates and established the chordate status of the tunicates. In 1867, Kovalevsky extended the germ layer concept of Christian Heinrich Pander and Karl Ernst von Baer to include the invertebrates, such as the ascidians, establishing an important embryologic unity in the animal kingdom. This was important evidence of the evolution of living organisms. In the Descent of Man (1871), Charles Darwin took serious note of Kovalevsky’s interpretation of the embryonic development of ascidians, writing:
M. Kovalevsky has lately observed that the larvae of the Ascidians are related to the Vertebrata in their manner of development, in the relative position of the nervous system and in possessing a structure closely like the chorda dorsalis of vertebrate animals; and in this he has since been confirmed by Prof. Kupffer. M. Kovalevsky writes to me from Naples, that he has now carried these observations further; and, should his results be well established, the whole will form a discovery of the greatest importance. Thus if we may rely on embryology, ever the safest guide in classification, it seems that we have at last gained a clew in the source whence the vertebrates were derived. I should then be justified in believing that at an extremely remote period a group of animals existed, resembling in many respects the larvae of our present ascidians, which diverged into two great branches – the one retrograding in development and producing the present class of Ascidians, the other rising to the crown and summit of the animal kingdom by giving birth to the Vertebrata.
Kovalevsky was elected to the Russian Academy of Sciences in 1890.