EDITORIAL NOTE. 



During the voyage of the Challenger, species of Siphonophorse were con- 

 tinually under observation in the living condition, both on the surface 

 of the ocean and in tanks on board the vessel ; none of the naturalists, 

 however, made any special study of this interesting and complicated 

 group of animals ; the specimens collected were merely preserved with 

 as much care and skill as was possible in the circumstances. 



Probably no class of marine organisms presents, in general, greater 

 difficulties in the way of examination than the Siphonophorse, and these 

 difficulties are increased many fold when the naturalist has to deal with 

 collections preserved in alcohol and other media, which contract and distort 

 the specimens. Indeed it was essential that any naturalist who would 

 undertake a successful examination and interpretation of these varied 

 forms should himself have investigated these organisms during many 

 years in the hiving state. 



Professor Haeckel, through his long-continued and elaborate investi- 

 gations of living Siphonophorae and Medusa? in the Mediterranean, Indian, 

 and Atlantic Oceans, was in a very special manner fitted to undertake such 

 a task, and it must be regarded as fortunate that he should have been 

 willing to undertake the work on condition that some of his own unpublished 

 observations should be incorporated. 



This important and masterly Report has thus become a Monograph of 

 the whole class, more complete than any hitherto published ; the classifi- 



