CHAMBERS'S INFORMATION FOR THE PEOPLE. 



round the coast of Britain, hanging from the 

 under-side of rocks between tide-marks. They 

 are all marine. The second group, the Hexac- 

 tinellidtF, so called from their spicules, which are 

 always silicious, having usually six rays, seem to 

 be confined to the deep sea, and are very abun- 

 dant there. In this family we have some of the 

 most singular and the most beautiful of natural 

 objects. Venus' flower-basket (Euplectella asper- 

 V/////W*), from the seas of the Philippine Islands, \ 

 is like a graceful horn-of-plenty wrought in an 

 infinitely delicate tissue of spun-glass. Hyalonema, 

 the Glass-rope Sponge of Japan, produces, grow- 

 ing downwards from the centre of a small conical 

 sponge, a great wisp of glassy spicules, as thick 

 as knitting-needles, and a couple of feet long, 

 which penetrate the mud, and hold the sponge in 

 its place, like a root. The upper part of this 

 ' glass-rope ' is almost always covered with a crust 

 formed of a spreading zoophyte. This is a case 

 of ' commensalism ' (Lat con, together ; mensa, a 

 table), an economical arrangement which is not 

 at all uncommon in nature. Two animals live 

 together habitually, one taking advantage of the 

 excess of food procured by the other by means of 

 currents produced by its cilia or some other 

 like means, and doubtless contributing in some 

 way to the comfort or 

 support of its 'chum.' The 

 bath sponge is the type 

 of the Ceratospongice (Gr. 

 keras, horn), distinguished 

 by their soft flexible skele- 

 ton of horn. The sponge 

 of commerce is brought 

 up by divers from water of 

 moderate depth, the finest 

 coming from the coasts 

 of Syria and the Greek 

 Archipelago, the greater 

 number from the Bahamas. 

 The Corticatce (Lat. cor- 

 Extemal surface and sec- tex, bark) include the glo- 

 tional view of Living bular sponges, frequent in 

 Sponge. deep water, with a thick 



outer bark bristling with 



long spicules, which spring in sheaves radiating 

 from the centre. The Halichondrice (Gr. hals, the 

 sea, and chotuire, gristle) are the common sponges 

 of the coasts of Britain, very abundantly incrusting 

 stones and sea-weeds below tide-mark, and some- 

 times shooting up into independent branching tufts 

 or tubes. They are quite Crush, and unfit for any 

 use. Their skeleton is composed of a combination 

 of horny granules or fibres, with silicious spicules 

 of diverse and often very elegant forms. Nearly 

 all the Porifera are marine. One genus, Spongilla, 

 or fresh-water sponge, is common in the fresh 

 waters of Britain. 



CLASS V. INFUSORIA. 



The Infusoria are chiefly microscopic, and are 

 found in all stagnant waters, or in any infusion 

 which has been exposed to the air for some time 

 hence the name. They do not emit pseudo-podia. 

 They possess a mouth, which leads into a sort of 

 gullet, excavated in the soft gelatinous substance of 

 the body ; but this gullet is not continued into a 

 defined stomach or alimentary canal, the organic 



134 



matter introduced by the mouth passing into, and 

 mixing with the sarcodic substance of the animal. 

 The mouth is generally surrounded by cilia (vibra- 

 tile hair-like appendages), by which currents are 

 formed in the water, and food brought into it 

 In the body are a number of contractile vesicles, 

 which pulsate at 

 regular intervals, 

 and may repre- 

 sent a rudimen- 

 tary heart Bur- 

 saria swims freely 

 about by means of 

 the cilia placed all 

 over its surface. 

 The Bell Animal- 

 cule, or Vorticella, 

 is attached, and 

 remains fixed like 

 a plant.' The body 

 is bell-shaped, the 

 opening of the bell Group of Vorticellidas. 

 being surrounded 



with a ring of cilia, which, by their vibratile move- 

 ments, bring food within reach. It is situated on 

 a long stalk, which is capable of spiral contraction. 

 This takes place on the slightest movement or 

 alarm. 



Bacteria, Spontaneous Generation. If a little 

 weak wine, or a thin syrup of sugar, or an infusion 

 of tea or of meat, be left exposed to the air, it 

 very soon begins to ferment or to putrefy. In 

 doing so, it becomes muddy ; and if a drop of the 

 muddy liquid be placed under a microscope, it 

 is found to contain myriads of excessively small 

 living and moving beings, most of which must be 

 referred to the Protozoa, though some are the 

 germs of different kinds of mould (fungi). Two 

 kinds are almost universal in such- solutions 

 minute, transparent, oval bodies, slightly enlarged 

 at each end, called bacteria; and very small rods, 

 generally of two joints, called -vibriones. No 

 structure can be made out in either of these, but 

 they are recognisable and distinguishable from 

 other things, and they have a peculiar vibratile 

 motion. A question has arisen, whether these 

 creatures, which appear everywhere, are all pro- 

 duced from germs of already existing creatures of 

 the same kind, or whether they may originate in 

 the liquid by the uniting of the substances required 

 to form them, which are all contained in the liquid, 

 the product then becoming alive. This latter 

 process has been called ' spontaneous ' or ' equivo- 

 cal' generation. Does life ever originate in such 

 a way? The following considerations seem to 

 render it improbable. 



If a ray of sunlight pass through a chink, and 

 traverse a dark room, its path is made evident 

 as a long gray line of motes dancing in the vibrat- 

 ing air. These motes settle down as dust ; and 

 if a little of this be magnified, it is found to be 

 mainly broken particles of wool and grains of 

 starch ; but it contains germs as well ; for if a little 

 dust be shaken into an infusion, we have a crop 

 both of animals and plants at once. Here, then, 

 is a source of germs which is universal. M. 

 Pasteur, a French chemist, has shewn that if a 

 flask be filled with a solution in which, if it were 

 left open, bacteria would abound immediately ; 

 and if it be entirely freed by heat from living 

 germs and air containing such, and the neck of 



