VETUS e T 
Structure of Marine Sponges. 335 
prolongations of the sponge-structure (often more than a dozen), 
which, tentacula-like, rose upwards all round to form the 
dome-like prominence of the head during projection—that, 
also tentacula-like, they ended in tongue-like terminations, 
but that these terminations were tied together by the invest- 
ing layer of transparent dermal sarcode, which thus transformed 
the whole head into a convex cribriform structure into which 
the floating particles of the vicinity were observed to be drawn, 
as, on the contrary, they were observed to issue from the pores 
or vents with single circular aperture. : 
(On removing the calcareous shell of the Balanus by acid 
and drying the remainder, these little heads, which presented a 
White colour, were found to be wide at their base where they 
joined the sponge, then constricted so as to form a neck, and 
