AND PHYSIOLOGY OP THE SPONGIADH:. 
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1. Those which have the skeletons constructed of keratose fibre only, as in the best 
cup-shaped Turkey sponges of commerce. 
2. Those having skeletons of arenated keratose fibre, as in the genus Dysidea. 
3. Those which have the skeleton formed of spiculated keratose fibre, as in Halichon- 
dria oculata, Johnston, Chalina, Geant, and in the common West Indian sponges of 
commerce. 
In the first Order no earthy material of any kind enters into the structure of the skeleton. 
The sponges of the second Order, by a natural transition, pass into the nearly allied 
great division of the Halichondroid skeletons ; the inability of the former to secrete 
silex in an organized form connecting them closely with the pure keratose, while the 
instinctive habit of appropriating extraneous matters recognizes the necessity of other 
material in the skeleton beside pure keratode ; and the secretion of it by its own inherent 
power appears to be the next natural step in the development of the animals. 
In the third division, those having the skeleton formed of spiculated keratose fibre, 
the gradual development is also well marked, as in one group we find spicula only in the 
primary or radiating fibres of the skeleton, while in another group they are found in 
both the primary and secondary fibres, and are developed simultaneously with the kera- 
tode of the young fibres of the skeleton. 
The second Order, the Siliceae, comprises those sponges in which the primary essential 
material of the skeleton consists of siliceous matter ; and this also may be divided into 
three sections or families. 
1. Those sponges which have the skeleton composed of solid siliceous fibres, as in 
Dactylocalyx jyumicea^ Stutchbuey. 
2. Those in which the skeleton consists of spicula dispersed without order on mem- 
branous surfaces, as in Hymeniacidon caruncula, Boweebank. 
3. Sponges having the skeleton consisting of spicula cemented together into a network 
by keratode, as in Halicliondria ^anicea, Johnston. 
The third Order, the Calcarese, has the primary essential material composed of calca- 
reous matter, and this division contains but one section or family : — 
Spicula dispersed without order on membranous surfaces, as in the genus Grantia as 
defined by Johnston. 
1. Keratosse ... a. Keratose fibre only. 
b. Arenated keratose fibre. 
c. Spiculated keratose fibre. 
2. Silicese a. Solid siliceous fibre. 
b. Spicula dispersed on membranes. 
c. Spicula cemented together by keratode. 
3. Calcareae ... a. Spicula dispersed on membranes. 
SjyicVjla of the Skeleton. 
The spicula in the skeletons of the Spongiadae appear to be the homologues of the 
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