426 HISTORY OF 



multitude of cells, which at last assume the appearance of a 

 plant or flower, are formed. 



If we may be led in this subject by analogy, it is most proba- 

 ble, that the substance of coral is producea in the same manner 



Sponffes have afforded a field for philosophical observers, and may be num. 

 bered amongst the most obscure or doubtful productions of nature. By 

 some they have been supposed the fabric of certain worms allied to tere. 

 bell*, which are often found straying' about in cavities ; an idea not very 

 probable, and which is now sufficiently exploded. Others have imagined 

 them to be mere vegetables ; but that they are really possessed of a living 

 principle seems evident from the circumstance of their alternately contract- 

 ing- and dilating their pores, and shrinking in some degree from the touch 

 when examined in their native waters. In short, sponges consist of an in- 

 finitely ramified mass of capillary tubes, possessed of a certain degree of 

 contractile po«er, and capable from their structure of absorbing nutriment 

 from the surrounding fluid in wliitli they are by nature immersed. They 

 therefore form an animal tribe different from all others, and may be consi- 

 dered as the most torpid of all zoophytes. 



The Funnel Sponge. — This species is funnel-shaped, and flexible, with the 

 surface more or less roughened and irregular. It is found both in the Medi- 

 terranean and Indian seas ; adhering, like others of its genus, to rocks. In 

 size it varies from a few inches in diameter to that of a foot or more. Its 

 colour is pale brown, and its substance less strong or tenacious than that of 

 the common or ofhcinal species. 



Tlie I'orticella, or Wheel Animals, are the most remarkable of all ani- 

 malcules, not only in their structure, but also in their habits and produc- 

 tion. In general form they bear a great affinity to the polypes, having a 

 contractile, naked body, furnished with rotatory organs round the mouth ; 

 and indeed many microscopical writers have denominated them clustef 

 polypes. They are almost invisibly minute, and generally found in clear 

 stagnant waters, during the summer months, attached to the stalks of the 

 lesser water plants, where they feed on animalcules still smaller than them- 

 Bclves. Many of the species are found in groups, sometimes formed by the 

 mere approximation of several individuals, and at other times by the rami, 

 fied or aggregate manner in which they grow. Tneir various motions, like 

 those of the polypes, are generally exerted only for the purpose of obtaining 

 prey. The rotatory motion of their tcntacula cause an eddy in the water, 

 around each individual, sufficient to attract into its vortex such animalcules 

 as happen to swim near ; these the little creature seizes, by suddenly con ■ 

 tracting its tentacula, and inclosing them in the midst. In several of the 

 species the stems, into which tliey occasionallv withdraw themselves, ai-e 

 somewhat rigid or scaly. The young are carried in oval integuments on 

 the outside of the lower part of the stems, and when ready to issue forth, 

 the parents aid their extrusion, where such is necessary, by writhing their 

 bodies, or strikin? the little vesicle. As soon as the young one is liberated 

 from its prison, it fixes itself, and commences the necessary operations to 

 procure its food. The infusory animals of Linnaeus are extremely simple in 

 their form, and generally invisible without a magnifying power. They are 

 eliiefiy found in infusions of animal and vegetable substances. 



