of a polyp. The subsequent change of heteromorphic generation, 

 from which more highly organized medusa develop must be 

 regarded as a generic form and is considered, consequently, 

 factually proved" (pp. 425 - 426). 



A preliminary report on these observations Krohn included 

 in a letter addressed to Miiller.47 



Figure 42. Planula hydromedusa Cladonema (A) and the 

 polyp developed from it Stauridium (B) by 

 Krohn . 



Two years later Krohn published a report about the 

 structure of the early stages of development of the medusa 

 Pelagic. noctitucaA^ At first he found near Messina invertebrate 

 medusae similar to ephyra scyphomedusa, separating from "polyp- 

 form helminths" (scyphistoma) , and he found also earlier larvae. 



47. A. Krohn, "Uber einige niedere. Thiere. Brief liche 

 Mitteilung a. d. Herausgeber, " ARCH . ANAT . , PHYSIOL 

 C1853) , pp. 137 - 141. 



48. A. Krohn, "Uber die friihesten Entwickelungsstufen der 



Pelagia nootiluca," 

 pp. 491 - 497. 



ARCH. ANAT., PHYSIOL. (1855), 



568 



