OAKS N _ LIVERPOOL BIOLOGICAL SOCIETY. 
at the first glance two very different tissues. The one is 
strong, fibrous and full of spicules, the other one is highly 
porous and reticulated, with a smaller number of spicules. 
The latter chiefly forms the choanosome, the former the 
ectosome, but broad strands of the ectosome are given off, 
which project down and branch throughout the choano- 
some, thus giving a strong support to the soft tissue of 
the choanosome (PI. XI., fig. 2). The incurrent and ex- 
current canals are large and numerous. The size of the 
flagellated chambers is about 0°04 by 0°028 mm. 
If one sees only the two extremes in the mode of growth 
of Cliona celata, the small boring form, which scarcely pro- 
jects out of the holes of a perforated oyster shell, and the 
large massive form described above, then it is really diffi- 
cult to convince oneself of the identity of the two forms. 
Intermediate stages, however, soon show the identity. 
The Zoological Museum of University College, Liverpool, 
possesses a specimen, dredged by Professor Herdman in 
Cailliach Bay, Mull, September, 1882, which represents 
an exceedingly good example of such an intermediate stage. 
The pore-areas of the future massive form are all fully 
developed, but they are easily recognized as being the 
upper surfaces of small papille which project from the 
holes of the perforated foreign body. Further, there is a 
layer of sponge-mass (varying from 1 to 3 mm. in thick- 
ness) outside and above the non-perforated surface of the 
foreign body (an igneous rock), which layer extends 
laterally to and fuses with the papille. 
After the boring form of Clrona celata had been described 
by Grant and Nardo, Johnston discovered the massive 
stage and recognized it as a variety of the boring one. 
Other authors again considered both forms as different 
species, so also Bowerbank, who established a new 
genus for the massive form and called it Raphyrus Grifith- 
