THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTOEY, 



[SIXTH SERIES.] 

 No. 21. SEPTEMBER 1889. 



XXI. — On the Organism of the Siphonojiliora and their 

 Phylogenetic Derivation : a Criticism iqyon E. HaeckeVs 

 so-called Medusome-theory . By Professor Carl Claus *. 



As is well known, opinions as to the interpretation of the 

 Siphonophora diverge in two directions, a number of natu- 

 ralists regarding them, after the example of C Vogt and li. 

 Leuckart, and in accordance witii the latter 's theory of poly- 

 morphism, as free-swimming Hydroid-stocks with Polypoid 

 and Medusoid individuals, while other zoologists adhere to 

 the older conception of Eschscholtz and Huxley, and, aided 

 by the image of a proliferating Sarsia (Metschnikoff), refer 

 the organism of the Siphonophore to the Medusa. I endea- 

 voured, as long since as 1860 f, to demonstrate the correctness 

 of the former view ; but more recently, in two memoirs, I 

 have pointed out what is common to the two theories and 

 sought to combine them. The same thing has lately been 

 done, although partly from other points of view, by Ilaeckel 

 in his ' Report on the Sipiionophorge collected by H.M.S. 

 * Challenger ' during the years 1873-76,' so rich in descrip- 



* Translated from a separate copy, furnished by the Author, of the 

 memoir published in the ' Arbeiten des Zoologischen Instituts der Uni- 

 versitat Wien,' tom. viii. Heft ii. pp. 159-174 (1889). 



t " Ueber Physophora hydrostatica,^'' in Zeitschr. f. wiss. Zool. Bd. xii, 



Ann. & Mug. N. Hist. Ser. 6. Vol. iv. 13 



