798 



PROF. A. DENDY AND MR. R. W. H. ROW OK 



genus Leucosoleoiia, which admittedly stands at the bottom of 

 the line of evolution of the Calcarea, both tyj)es of collared cells 

 exist, but apparently not side by side in the same species ; and 

 Ave find further, that the two pidncipal lines of descent, which 



Text-fio-. 133. 



PHARETRONES"' 



AMPHORISCID.^ 



HOMOCOELID/E 



PHYLOGENY OF CALCAREOUS SPONGES. 



appear, on quite other grounds, to have sprung from the homocoel 

 sponges, are characterised respectively by the two types of 

 collared cells. It is interestine- to note that these two main lines 



