rich in the zoological material of the sea — Naples, Messina, 

 Nice, Madeira — and using, in particular, those subjects on 

 which Krohn made many important observations leading to 

 serious theoretical meditation. Kovalevsky later cited with 

 respect the works of Krohn on the structure of sagitta and 

 the development of tunicates, and Mechnikov cited his works 

 on the development of coelenterates and echinoderms . 



In the preparation of that revolution in embryology 

 which was accomplished by Kovalevsky and Mechnikov, converting 

 the comparative-descriptive embryology into comparative 

 evolutionary embryology, Krohn 's modest investigations played 

 their role, and therefore his name must not be forgotten in 

 the history of Russian science. 



598 



