766 
DE. J. S. BOWEEBANK ON THE ANATOMY 
Boweebank, ms., represented by figs. 2, 3, 4, 5, 6, & 7, Plate XXIX. The first of these 
(fig. 2) represents a short variety of the normal spinulete form. In the second (fig. 3) we 
have a bi-spinulate, and in the third (fig. 4) a tri-spinidate form. The latter two are not 
mere malformations, but they prevail to a great extent in the structures of the sponge, 
subject to variations in the distances in the development of the second and thhrd inflations 
from the basal one. Figs. 5, 6, & 7 represent immature spicula in progressive stages 
of development, the apices having hemispherical terminations. 
Auxiliary Sjpicula. 
Beside the spicula essential to the structure of the skeleton there are several other 
forms of these organs, many of which, although not absolutely necessary in the structure 
of the skeleton, are of very frequent occurrence in subsidiary organs found in particular 
species and in peculiar genera. They may be conveniently classed under the following 
heads : — 
Connecting spicula. 
Prehensile spicula. 
Defensive spicula. 
Tension spicula. 
Retentive spicula. 
Spicula of the sarcode. 
Spicula of the gemmules. 
In the above designations of the auxiliary spicula, it must not be understood that their 
respective titles strictly define their offices, as it frequently occurs that under peculiar 
circumstances the same form of spiculum is destined to serve two, or even three distinct 
purposes. Thus, an external defensive spiculum will occasionally perform retentive 
offices for the purpose of securing prey ; or internal defensive spicula will combine the 
offices of defensive spicula against the larger and more powerful of their enemies with 
that of wounding and securing their smaller ones. 
The Connecting Spicula. 
The normal form of the connecting spicula is that of an elongate shaft, with a ternate 
apical termination. But all the varieties of this form are not necessarily connecting spicula. 
Some of them subserve the offices of external or internal defensive organs, as I have de- 
scribed elsewhere. The varieties that may correctly be designated by this title are those 
which I have termed in the first part of this paper expando- and patento-ternate spicula, 
and some varieties of the recurvo-ternate form also appear to be applied to this peculiar 
office. Their situation in the sponge, rather than their precise form, determines their 
title to be thus designated. Nor is their especial purpose of connecting the dermal 
crust of the sponge with the great mass of the skeleton beneath, the only office they are 
destined to perform in the economy of the animal, as their ternate terminations are so 
disposed as to form a series of reticulations and areas for the support of the vahailar 
membranes of the proximal ends of the intermarginal cavities of the sponges, in which 
