articles Krohn disproved the erroneous data of Milne-Edwards 

 and Sars and confirmed the observations of Mechnikov that the 

 larva of Botryllus possesses the same simple structure as 

 that of the solitary ascidian and undergoes analogical 

 metamorphosis. After settling on the bottom, the young 

 Botryllus , already in the process of transformation, produces 

 a bud from which a second individual originates, which in 

 turn begins to bud. As a result a stellate colony is obtained. 

 The budding of the colonial ascidian is represented in the 

 second article, in which Krohn compared its details with the 

 corresponding phenomena in salpa. 



With these fragmentary investigations of vegetative 

 multiplication, Krohn' s scientific activity apparently came 

 to an end. In the following years (1870 to 1880) his reports 

 were regularly placed in journals, but no works appeared after 

 this time. 



For thirty-five years he collected facts from the field 

 of anatomy and embryology, mainly of invertebrates, covering a 

 very great number of systematic groups CI 40) . His embryological 

 works (including descriptions of larvae and means of reproduc- 

 tion) concerned coelenterates, nemerteans, annelids, molluscs, 

 crustaceans, echinoderms, and tunicates. 



Krohn did not belong to those investigators paving new 

 roads in science. All his comparative-anatomical and comparative- 

 erabryological remarks are concerned with the comparison of 

 closely related forms. Comparing, for example, representatives 

 of different classes of echinoderms and establishing the 

 features of similarity and difference between salpa and 

 ascidians, Krohn did not offer sympathy either to the theory 

 of types, nor to the idea of unity of planes, nor to evolu- 

 tionary study. Krohn cited Darwin only in his works on the 

 structure and development of cirripedes, highly rating his 

 monograph dedicated to this order of crustacean. 



Besides this, evidence exists about Krohn' s deep interest 

 in the investigations of A. 0. Kovalevsky, who established the 

 similarity of the embryonic development of ascidians and 

 vertebrates. The first report by Kovalevsky dedicated to the 

 development of ascidians was published in 1866 in ZAPISKAKH 

 PETERBURGSKOI AKADEMII NAUK (Notes of the Petersburg 



594 



