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FOSSIL PORIFERA. 219 
ized mass or axis, each polype having an independent exist- 
ence, and exhibiting volition and perception, in a greater or 
lesser degree. 
FossiL PoRIFERA. 
The terms Amorphozoa (signifying animals of variable 
shapes), and Porifera (structures traversed by pores or chan- 
nels), are employed by naturalists to designate the Sponges 
and analogous organisms, which appear to occupy the boun- 
_ dary line that separates the animal from the vegetable 
kingdom. The true position of the Sponges in the great 
system of Creation is still a disputed point ; for while many 
- distinguished naturalists regard them as Protozoa, or the 
lowest type of animal organization, others of equal eminence 
affirm that neither in structure nor functions do they differ 
from vegetables in any essential particular; and that if a 
line be drawn between the two kingdoms the Porifera must 
be placed on the vegetable side of the boundary. On the 
other hand, Dr. George Johnston, in his delightful work on 
the British Zoophytes,* expresses his opinion that there 
is nothing to discountenance the belief that these bodies 
hold an intermediate place ; that they are, in fact, the true 
Zoophytes, or animal-plants ; in some forms, as the green 
Spongille of our lakes, the vegetable nature prevails ; while 
in others, as the horny or keratose sponges filled with muci- 
laginous slime, and the fleshy Z'ethya whose oscula, or pores, 
are said to exhibit signs of irritability, the animal character 
predominates. 
Without committing ourselves to either opinion, and 
_ simply remarking that the large proportion of silex that 
enters into the tissues of a considerable number of the porifera, 
* A History of British Sponges, &c. by Dr. George Johnston, Edin- 
burgh. 1843. One vol. 8vo. with twenty-five plates. A previous 
work, “A History of British Zoophytes,” with forty-four plates, from 
drawings by the accomplished lady of the Author, cannot be too 
_ highly commended. 
