SPONGIDA. 65 
habitually destitute of cellular structure. Their bodies are formed 
of a sort of animated jelly, amorphous and diaphanous, which has 
received from Dujardin the name of Sarcode. 
Infinitely varied in their form, the Protozoa are chiefly charac- 
terised by the absence of a nervous system, of organs of sense, and in 
many of them the existence of a distinct alimentary system is still to 
be ascertained. The more highly organised of the group possess 
vibratile cilia, which act as organs of locomotion as well as enable 
them to collect their food. Their bodies are sometimes naked, some- 
times covered with a siliceous, chalky, or membranous shell, and in 
some covered with cilia, and in the cortical layer of a species of 
Bursaria, Professor Allman has detected urticating filaments. The 
Protozoa may be divided into the Sfongida, the Rhizopoda, and the 
Lnfusoria. 
I.—SPoNGIDA. 
_ The sponge is a natural production, which has been known from 
times of the highest antiquity. Aristotle, Pliny, and all other writers 
who occupied themselves with natural history in ancient times, are 
agreed in according to it a sensitive life. They recognise the curious 
fact that the sponge shrinks from the hand which tries to seize it, 
and clings to the rocks on which it is rooted, as if it would resist the 
efforts made to detach it. Pliny, Dioscorides, and their commen- 
tators, even formed the idea that sponges were capable of feeling, 
and that they adhered to their native rock by special force. They 
even distinguished males from females. Erasmus, however, criticising 
Pliny, concludes that he may pass over all he has written upon the 
sponge. The sponge, in short, was to the ancients something 
between a plant and an animal. 
Rondelet—the friend of the celebrated Rabelais, whom the merry 
curate of Meudon designated under the name of Rondibzlis—who was 
himself a physician and naturalist of Montpellier, denied at first the 
existence of sensibility in sponges. He originated the idea that 
these productions belonged to the vegetable kingdom—an idea which 
Tournefort, Gaspard Bauhin, Rey, and even Linnzus in the first editions 
of his ‘Systema Nature,” supported by the great authority of their 
names. Afterwards, influenced by the convincing labours of Trembley 
and some other observers; Linnzeus withdrew the sponges from the 
vegetable kingdom. He satisfied himself, in short, that certain polyps 
much resembled sponges in the nature of their parenchyma, and that, 
on the other hand, the grouping of sponges with plants was not such 
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