218 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 papillae which project from the 

 holes of the perforated foreign body. Further, there is a 

 layer of sponge-mass (varying from 1 to 3 nnn. 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 papillae. 



After the boring form of Cliona 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 njassive form and called it Raphjrus Griffith- 



