THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 90. JUNE 1865. 



XLVI. — On a new Fo?'m of Alternation of Generations in the 

 Medusa, and on the Relationship of the Geryonidas and iEgi- 

 nidas. By Dr. Ernst Haeckel*. 



The fact of the alternation of generations between the Medusa? 

 or Discophorous Acalephs and the Hydroid polypes, which when 

 first made known excited so much attention, and was doubted 

 by so many, has in the two last decennia been proved, by widely 

 extended investigations, to be so generally diffused in the class 

 of the Hydromedusse, that the cases of simple homogonic re- 

 production in this class of animals appear to constitute rare ex- 

 ceptions. At the same time, an unexpected abundance of the 

 most various modifications has been discovered, rendering the 

 reproductive conditions of these animals the most interesting in 

 the whole organic world. But that this abundance is still by 

 no means exhausted is proved by almost every thorough investi- 

 gation of a particular group of Medusas. Thus the careful in- 

 vestigations which I had the opportunity of making during a 

 long period last spring, in the Gulf of Nice, upon a large Ge- 

 ryonia, and of continuing up to the present time upon well- 

 preserved preparations, have led me to the discovery of a new 

 form of alternation of generations, which differs so much from 

 all other known forms that it is certainly permissible to give a 

 short preliminary account of it here. 



The Geryonidce form a family of the Craspedota or Medusa 

 cryptocarpa, which, although small, is strikingly distinguished 

 by many remarkable structural characters. The family may be 

 divided into two subfamilies — the Liriopides and Carmarinides — 

 of which the former (Liriope, Glossocodon) resemble most of the 

 other Medusas in the quadruplicity of all their organs, whilst the 



* Translated from the ' Monatsbericht der Akad. der Wiss. zu Berlin,' 

 Feb. 1865, p. 85, by W. S. Dallas, F.L.S. 



Ann. fy Mag. N. Hist. Ser.3. Vol.xv. 30 



