268 



♦ KNOWLEDGE ♦ 



[July 1, 1886. 



biological research. And development by cell-modification 

 applies to the body throngliout, to bone, to cartilage, and 

 sinew, as well as to the myriads of nerve-tissues, varying 

 between the fifteen-hundredth and the twelve-thousandth 

 of an inch in breadth, that keep us in touch with the 

 universe. But, easy as it is to dissect and describe the 

 nervous mechanism, the nature of the connexion alike 

 between nervous imjiulse and consciousness in a man, and 

 between sensation and contractile action in a moneron, 

 remains an insoluble mystery. 



What has been said concerning the dilfased sensitiveness 

 of the lower animals adds force and suggestiveness to 

 Hjeckel's remark, quoted in a former chapter, that the plant 

 sealed its fate, limiting the action of the outer world upon 

 it, when the protoplasm enclosed itself within a wall of 

 cellulose. This isolation, or lessened susceptibility to the 

 vibrations of air and ether, to changes of temperature, and 

 a thousandfold subtle influences, the animal escaped by 

 remaining mobile and setting up no barriers between itself 

 and its environment. 



A short step upward from the moneron brings us to the 

 Anueha (Gr. iimoibe, change), so called from its constant 

 change of shape as it protrudes and withdraws the pseudo- 

 pods. It shows approach towards unlikeness in parts, from 

 the simple to the complex, in the modification of the proto- 

 plasm into a membranous skin at the surface, and in a 

 nucleus near the centre, with an expanding and contracting 

 cavity for distributing food and oxygen in the body — a 

 primitive apparatus for digestion and circulation. Therein 

 is the beginning of a division of function, of a distribu- 

 tion of labour, leading to cell-modification into organs. 

 8ome of the lowest amfcbii' secrete, like the diatoms among 

 plants, solid matter from the sea, building for themselves 

 primitive organs of shelter and defence in the shape of 

 exquisitely-formed chambered shells pierced with holes 

 through which the soft body is connected and the pseudo- 

 pods pushed for capture of food, which, as throughout the 

 animal kingdom, consists of organised matter. Some form 

 theu" skeletons of lime, others of flint, evidencing to the 

 possession of a selective power or affinity by even the 

 minutest creatures, and it is these skeletons of ancient 

 foraminifera' that compose vast beds of organically-derived 

 strata. 



Still more marked advance towards unlikeness in parts is 

 shown in the Infusoria, so called because readily developed 

 in infusions of exposed vegetable matter, wherein they 

 crowd by myriads in the space of a water-drop. Instead of 

 the pseudopods of the moneron and the amosba, we find 

 vibrating filaments or cilia, by which supplies are swept into 

 the body, which is furnished with an opening or indimen- 

 tary mouth and short gullet, through which the food and 

 oxygen pass to the body-cavity. The protozoa which are 

 free to move about can pi'ocure their food and oxygen easily, 

 but such as are rooted to one spot have to develop special 

 organs for securing these necessaries of life. These we find 

 provided in the colonies of amceba? known as Sponi/es, which, 

 however, stand midway between the first and second sub- 

 kingdoms, since division of labour is further developed in 

 them, and traces of a nervous system are found among cer- 

 tain species. Very lovely are the .skeletons which some of 

 them secrete, such as Venus's flower-basket with its graceful 

 fretted spirals ; but more familiar to us are the useful fibrous 

 and porous domestic sponges woven of material said to be 

 chemically allied to that spun by silkworms. The amceba^ 

 living on the outside of the s])onge can procure food and 

 oxygen easily; not so those living in the inside, and to effect 

 this they have developed cilia, the whiplike action of which 

 drives the water, charged with food and oxygen, through the 

 innumerable canals, whence, having served its pur])Ose, it 



is driven out, through other canals, carrying the refuse from 

 the amu'ba; with it. The whole sponge represents, as has been 

 aptly said, a kind of submarine Venice, " where the people 

 are ranged about the streets and roads in such a manner 

 that each can easily appropriate his food from the water as 

 it pa.sses along." 



II. CffiLESTEi{AT.\. — Speaking broadly, all the animals 

 included in the first sub-kingdom are made up of single 

 cells united together, but like one another ; no\y we find 

 the animals made up of many cells more or less modified 

 into ti.ssue, although still of low organisation, one evidence 

 of which is that, like the protozoa, they have no vital parts, 

 and that there is no separate canal for absorbing food and 

 carrying away refuse, the mouth still opening direct into the 

 body-cavity. 



The lowest representatives of the " hollow-bodied " are 

 the tiny cup or tube shaped, jellylike, green-hued polyps 

 named Ili/dra, which, with theii- budlike clusters of young 

 — soon to start in life on their own account — are found 

 clinging, mouth downwards, to weeds and rubbish in fresh 

 water. From the mouth hang a number of tentacles con- 

 tainmg cells, in which lie liarbed threads coiled up in a 

 poison fluid. When anything touches these tentacles they 

 contract, the cells burst and fling the threads, lassolike, 

 around the prey, poisoning it with the fluid. From some of 

 the marine species which secrete tubes of flint and project 

 themselves therefrom like flowers, so that the sea-depths are 

 covered wdth their waving, plantlike forms, the buds 

 detach themselves, and become the beautifully tinted 

 Medusiv. or jelly-fish. These produce eggs which become 

 rooted polyps, so that the ofl'spring never resembles its 

 parents, but always its grandparents. All living matter is 

 largely made up of water, the average proportion ranging 

 from seventy to ninety per cent., but in the jelly-fish it is 

 about -lOO to 1. Yet, fragile as is the creature, its structure 

 is complex. Canals traverse the swiniming-bell, and carry 

 food and oxygen to every jiart ; rudimentary muscles in the 

 shape of contractile tissues propel the animal along, in 

 rhythmic grace of motion ; a nervous system runs round the 

 margin of the bell ; there are rudimentary eyes in beadlike 

 pigment-spots, and rudimentary ears in small sacs also along 

 the margin ; and the hanging tentacles are charged, as in its 

 fresh-water ally, with deadly fluid. 



Lovelier still, and of slightly more complex structure, are 

 the variously coloured Sea Anemones, with their petal-like 

 tentacles ; while nearly allied to these are the colonies of 

 Coral-hvilders, which, despite the surging wave and drifting 

 current, raise their treelike structures, foundations of solid 

 land on which the bird will build her nest and man set his 

 dwelling. 



III. EcHixuDERMA'iw. — This division includes all rayed 

 animals, the skin being hardened by the secretion of jointed 

 or leathery plates, or of spines or hedgehog-like prickles. 

 In some, as the Starfi,sh, the luys spring from a common 

 centre ; in others, as the Sea-urchin, they are coiled to form 

 a globular body ; in the Sea-lilies, which abounded far back 

 as Silurian times, but which are now rare, they spring, 

 ttowerlike, from the end of a fixed stalk ; in the sluglike 

 Sea-mcumbers, which possess the power dyspeptics may envy 

 of throwing away the inside of the body and gi-owing it 

 anew, the skin is tough, the limy matter being secreted in 

 scattered spicules. 



All the eohinoderms have the alimentary canal shut off" 

 from the body-cavity, involving special provision for nutri- 

 tion. This is effected by a number of canals which com- 

 municate with the outside of the body, and through which 

 the sea-water is driven by cilia, as in the sponges. The 

 water is also pressed from the canals into numei'ous little 

 suckers, bv which the animal crawls along — nature's first 



