33 



flesh is entirely got rid of, and the sponge, in its well- 

 known commercial form, is the residuum. 



Tt is with reference to the composition of the inorganic 

 framework left after the soft gelatinous tissues have been 

 removed that the sponges, as an entire group, are classified 

 by zoologists. All those in which the supporting frame- 

 work or skeleton is, as in the case of the bath sponge, of a 

 more or less flexible horn-like consistence, are relegated to 

 the order known as the horny sponges, or Ceratospoiigia. 

 In a second group, needle-shaped or variously modified 

 elements known as Spiaila, having a glass-like or silicious 

 composition, are either added to or entirely replace the 

 horny framework, and is consequently distinguished by the 

 name of the silicious series or Silicispongice. In a third 

 group, that of the Calcispongice, a spicula skeleton is like- 

 wise developed, but, as indicated by its title, is of a cal- 

 careous nature, the component spicules being composed of 

 carbonate of lime. A fourth or relatively small group 

 remains, in which a spicular, horny, or other skeletal 

 framework is entirely absent, the entire sponge body con- 

 sisting of the easily destructible gelatinous flesh, already 

 referred to as constituting the living element in the 

 ordinary sponge. For this least specialized group the title 

 of slime sponges or MyxospongicE has been proposed. The 

 diversity of external shape presented by the adult sponge- 

 stocks belonging to the several groups or orders above 

 enumerated are found to be almost infinite, the same 

 species, indeed, in a large number of instances, varying 

 indefinitely in this respect. Among the multifarious series 

 that exist, reference may nevertheless be made to some 

 half-a-dozen typical growth, forms which constitute, as it 

 were, a groundwork upon which all the other modifications 

 are built up. Thus, in a very large series of sponges, the 



[42] D 



