14 A Guide to the Zoological Collections in the 



pouches derived from the original gastral cavity to form 

 systems of canals and of chambers— the "ciliated cham- 

 bers " — in which all the digestive and respiratory work of 

 the sponge is carried on. In these cases the water carry- 

 ing food and dissolved air streams through the "pores" 

 into "afferent canals " which lead into "ciliated chambers" 

 that are really only special developments of the branches 

 of the gastral cavity. From the ciliated chambers the now 

 effete water passes through "efferent canals" into the 

 much-restricted gastral cavity, whence it streams out at 

 the osculum. 



This complicated branching canal and chamber system 

 can be seen in almost any sponge, but it is specially 

 well seen in the exhibited vertical section (spirit-speci- 

 men) of the Hexactinellid sponge Pheronema globosinn^ in 

 Case 1. 



Further complications of the sponge-form result from 

 the fact that many sponges increase by budding, so that 

 the originally single sponge becomes a colony of sponges. 

 This is well seen in the exhibited specimens of Sycandra^ 

 Reniera and Chalina. 



It has already been stated that a firm supporting skeleton 

 is usually developed in the mesoderm of the sponge, and 

 this skeleton, from the superficial observer's point of view, 

 is the principal part of the sponge, as it forms the bulk of 

 the animal and its roost enduring part. 



With the exception of one small Family — the Spongil- 

 lidae--2A\ the sponges are marine, living either attached to 

 rocks and reefs in shallow water, or anchored in the mud 

 of the ocean-depths. 



Sponges are divided into two great Classes — [\\Calcarea 

 and (2) Nun-Calcarea. 



I. PORIFERA CALCAREA. 



[€il5C 1]. 



The Calcarca consist of one Order, namely, — 



