208 THE AUSTRALIAN HYDROMEDUS^E, 



The recent researches of Kleinenberg (1), F. E. Schulze (2), 

 Hertwig (3), Weismann (4), Haraann (5), Jickeli (6), myself (7), 

 and others on the structure of the Hydromedusae, have thrown 

 quite a new light on these animals. With the aid of these authors 

 results and with the help of Haeckel's (8), Monagraph, I hope to 

 be able to extend our knowledge on this subject a little. 



The great scientific interest which attaches to the study of the 

 Hydromedusa? and the nearly related Siphonophor-a, lies in the 

 Polymorphism of the individuals which belong to one colony. All 

 possible stages in the differentiation of the persons are met with, 

 and it is a thing of particular interest to follow the development 

 of this Polymorphism through its different stages. 



This Polymorphism is attained in the following manner : — The 

 Hydroids multiply by budding, and all pei-sonsor individuals, with 

 the exception of the free Medusa-stages, which bud from the 

 original Polype, remain in continuity, their stomachs are united by 

 a tube. Now a division of labour takes place among the different 

 persons and consequently they change their shape and structure by 

 natural selection, differing finally very much from each other. 



(1.) N. Kleinenberg. Hydra, 1S72. 



(2.) F. E. Schulze. Cordylophora lacustris, 1871- Syncoryne Sarsii, 

 1873. 



(3.) 0. und R. Hertwig. Das Nervensystem und die Sinnesorgaue der 

 Medusen, 187S. Der Organismus der Medusen, 187S. 



(4.) Weismann. Die Entstehung der Geschlechtszellen bei den Hydroiden, 

 1883. 



(5.) 0. Hamann. Der Organismus der Hydroidpolypen Jenaische 

 Zeitschrift. Band, XV. Seite. 545. 



(6.) G. Jickeli. Der Bau der Hydroidpolypen. I., II., Morpholo- 

 gisches Jahrbuch. Band, VIII Seite, 373, 580. 



(7 ) R. von Lendenfeld. Ueber das Nervensystem der Hydroidpolypen- 

 Zoologischer Anzeiger Nr. 131. Ueber eine eigentniimliche Art der 

 Sprossenbildung bei den Campanulariden. Zoologischer Anzeiger Nr. 130. 

 Ueber Wehrthiere und Nesselzellen Zeitschrift fur wiss. Zool. Band, 

 XXXVIII. Seite, 355. (Translated into English Annales ami Magazine 

 of Natural History. 5 Series. Nr. 71) Eucopella Campanularia Zeit- 

 schrift fur Wissenschaft. Zool. Band, XXXVIII. Seite, 497. 



(8.) K. Haeckel. Das System der Medusen. Jena, 1879-1880. Die 

 Medusen der Challenger Expedition. Jena, 1S81 (Translated into English. 

 Report of the Zoology of the voyage of the " Challenger.") 



