762 
DE. J. S. BOWEEBANK ON THE ANATOMY 
OEOANIZATION AND PHYSIOLOGY. 
Previously to entering’ on the subject of the organization and physiology of the Spon- 
giadse in detail, it will be necessary to take a brief view of the general structure of these 
animals. Whatever may be their form, or however they may differ from each other in 
appearance, there are certain points in their organization in which they all agree. In 
the first place, however variable in its form and mode of structure, there is always a 
skeleton present, on which the rest of the organic parts are based and maintained. 
Amidst the skeleton, and intimately incorporated with it, are the interstitial canals, con- 
sisting usually of two series ; the first appropriated to the incurrent streams of the 
surrounding water, and the second to the excurrent streams, which they conduct from 
the interior of the sponge to the oscula at its surface, through which they are discharged. 
In the event of the absence of the excurrent system of canals, their office is served by the 
great cloacal cavities that are found to exist in some forms of sponges, extending ffom 
the base to the most distant parts of the animal. Beside these large cavities, there are 
others of a much more limited character, the intermarginal cavities, which are situated 
immediately below the dermal membrane, and which receive the water inhaled by the 
sponge and transmit it to the mouths of the incurrent canals which have their origin in 
the intermarginal cavities. Enveloping the entire mass of the sponge we find the dermal 
membrane, in which are situated the pores, for inhalation and imbibition of nutriment, 
and the supply of the incurrent canals ; and the oscula, through which the excremen- 
titious matter and the exhausted streams of water are poured from the terminations of 
the excurrent canals. These parts are indispensably necessary, and are always present 
in a living sponge. The attachment of the Spongiadse to the body to which they adhere 
during life, is effected by a basal membrane which presents a simple adhesive surface, 
following the sinuosities of the body on which it is based, entering into holes or cracks 
and filling them up, thus securing a firm hold of the mass on which they are fixed. 
When it so happens that the locality consists of sand or mud, their bases frequently 
assume the form of branching roots, which penetrate the mud or sand to a considerable 
extent ; but they are never instrumental to the nutrition of the animal — they are simply 
the anchors by which it is fixed to its locality for life. 
The Skeleton. 
There are two important distinctive characters for consideration in treating of the 
structure of the skeleton : — 1st, the material of which it is constructed ; and 2nd, the 
mode of its arrangement. 
By selecting the material substance of the skeleton as the means of dividing the 
Spongiadse into Orders, we obtain three well-defined natural groups, which are again 
readily divisible into Families, based on the mode of the arrangement of the substance 
of which the skeleton is composed. 
The first Order, the Keratosse, consists of those sponges in which the primary essential 
material of the skeleton is keratose fibre. It may be divided into three families. 
