The supposition that they were stages of development of 

 Pelagia noctiluca was completely confirmed. After many 

 unsuccessful attempts, Krohn could carry out artificial 

 insemination. As a result of division ,larvae formed having a 

 cylindrical, usually stretched form (Tigure 43, A). The end 

 of the larvae (a) which is directed forward while swimming 

 is rounded, and the other (b) is chipped off. The surface of 

 the larva is covered by short cilia. In the blunt end occurs a 

 depression with an extremely small, round orifice is seen. 

 This orifice is the mouth, which leads to the round, clearly 

 outlined cavity of the stomach (c) , occupying the posterior 

 third of the body. Tne mouth and stomach, in Krohn 's words, 

 are already clearly differentiated already in the natural forms, 

 but it is still a non-hatched embryo. However in the present 

 stage the stomach is shorter and more rounded than in the 

 free larvae. 



Mechnikov rated highly this discovery by Krohn. In 

 his monograph EMBRYOLOGICAL INVESTIGATIONS ON MEDUSA 

 (1866), 49 he noticed the weak interest in embryology by the 

 zoologists of the mid-nineteenth century. He wrote: 



Even important generalizations, such as the similarity 

 between the two layers of coelenterates and the 

 embryonic layers of the higher animals, emphasized by 

 Huxley, and significant facts, such as Krohn' s discovery 

 of the formation of a stomach in pelagia by a 

 stretching of the blastomeres, remained without 

 attention and in a lower plane, (p. 284) 



The correctness of these observations by Krohn was later 

 confirmed by Kovalevsky and Mechnikov. In this work also, 

 Krohn reported one important discovery: "On the contrary to 

 Medusa aurita and other above-named medusae, "50 he wrote, 

 "Pelagia noctiluoa develops without the generation of 

 helminths" (p. 469). Krohn could trace how the swimming 



49. Cited in I. I. Mechnikov, IZBRANNYE BIOLOGICHESKIE 

 PROIZVEDENIYA (1950), pp. 271 - 472. 



50. Krohn compared the development of Pelagia with the 

 development of Medusa, Cyanea, Chrysaora, Cephea, and 

 Cassiopea . 



569 



