THE SIPHONOPHORA OF THE SIBOGA EXPEDITION 



BY 



ALBERTINE D. LENS and THEA VAN RIEMSDIJK, 



Utrecht. 



\\'ith 24 plates and 52 textfiguies. 



PREFACE. 



The enormous difficulties which accompany any attempt at systematic definition and 

 description of preserved specimens of the very delicate Siphonophora have been forcibly insisted 

 upon by Cnux in the preface to his work on the Siphonophores of the Plankton expedition (1897). 

 These difficulties are increased by the fact that the different forms and species are as yet in so 

 many respects still very imperfectly known and have often been insufficiently described. 



Moreover the literature of the subject is already very extensive (120 different titles are 

 cited in our list) and many articles are neither lucid nor exhaustive. Papers that have been 

 written by authors who have examined living specimens are often ver)' difficult to interpret for 

 those wo find themselves restricted to observations on preserved material. 



We have attempted to become acquainted with the specimens of former expeditions as 

 far as they are vet to be found in the different Museums. Of the Challenger SipJionopJiora the 

 British Museum contains no further remnants than a certain number of specimens of Rliodalia 

 niiratida Hkl. Of all the other species described in Haeckel's bulky volume — also of his 

 own private collection — no traces are left. 



We were informed by the Curator, Mr. R. Kirkpatrick, that Prof. Haeckel had written 

 to him, that a great number had been submitted to anatomical investigation and that the rest 

 had been in an unsatisfactory state of preservation. This may explain their present deficiency. 



We have also examined specimens that are contained in the Musee d'Histoire Naturelle 

 in Paris, in the Berlin Museum, in the Museum at Leipzig University and in the Museum of 

 Comparative Zoology at Cambridge, Mass. and in the aquaria of the Zoological Station at Naples. 



SIBOGA-EXI'F.DITIK IX. I 



