NARRATIVE OF THE CRUISE. 
645 
the question as to whether the given specimen is to be referred to this genus or to the 
other, the existence of an absolute distinction (in the sense of Nageli) is indispensable. 
“ The whole Report is almost exclusively of a critical character. Its most interesting 
positive statements are the following : — on the structure of the skeletal fibres and their 
development ; statements on the formations which Dr. Polejaeff feels inclined to connect 
with the filaments ; some statements of a more detailed character on the anatomical 
structure of the soft- parts; organisation of Darwinella, Ianthella, Psammoclema, 
Psammopemma, Carteriospongia, Phyllospongia, Luff aria, and Verongia; and data on 
the spermatogenesis in the last mentioned genus.” 
