SPONG7DA. 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 Spongida, the Rhizopoda, and the 

 Infusoria. 



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 cf Rondibilis 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 Linnaeus in the first editions 

 of his " Systema Naturae," supported by the great authority of theii 

 names. Afterwards, influenced by the convincing labours of Trembley 

 and some other observers, Linnaeus 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 net such 



