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THE NATURE OF SPONGES. 
(. Researches of Clark ancf Carter .) 
By HENRY J. SLACK, F.G.S. 
SECRETARY OE THE ROYAL MICROSCOPICAL SOCIETY. 
[PLATE LXXXIY.] 
T HE true nature of sponges has long be3n a puzzle to natu- 
ralists, and various opinions have been held concerning them. 
No one now supposes them to he members of the vegetable king- 
dom ; but, though their animality is decided, discussions are 
still going on as to the group with which they are most nearly 
connected ; and much light might be thrown upon the subject 
if more microscopists would watch the early stages and growth 
of either marine or freshwater forms. Spongillse, which belong 
to the latter, are known to most collectors, but few do more 
than make a rough examination of their structure, or mount 
gemmules as cabinet objects. 
Recent researches of Professor H. James Clark will help to 
stimulate enquiry into these interesting organisms ; but his last 
paper, which appeared in “ Silliman’s Journal,” and which is 
copied into the 66 Monthly Microscopical Journal ” for March, 
will scarcely be intelligible without some previous knowledge, 
and reference to other books. 
What is now proposed is to supply a sufficient popular ex- 
planation of the most interesting points, freed as much as 
possible from technical difficulties, and from details which be- 
ginners will best learn from actual study of the objects. 
Professor H. James Clark controverts the opinion of Haeckel 
and others, that sponges are essentially compound polyps, and 
he alleges reasons for associating them with flagellate, or whip - 
bearing, infusoria. 
In entering upon these subjects, it is necessary to form some 
idea of the more obvious characteristics of sponges, polyps, and 
whip-bearing infusorians. In the first place, it is well for the 
student to contemplate widely different sorts of sponge. Take, 
for example, a common toilet sponge— here is the skeleton of a 
sponge belonging to the keratose group. Its structure is what 
