July 1, 1886.] 



KNOWLEDGE ♦ 



267 



fProtoaoa (Gr. Protos, -first ; 

 zoon, animal) 



Cojlenterata vGr. Koilos, hol- 

 low ; ejUrron. bowel) 



Echinodermata (Gr. Echimxi, 

 a hedgehog: dcrm/i, skinj 



Annnlosa (Lat. Annulu-f, a 

 ling) 



^oUosca (Lat. Mollis, soft) 



Vertebr.ita (Lat. Ytrtebra, a 

 joint) 



Simplest forms 

 Hollow-bodied 

 Spiny-bodied 

 Joint- bodied 



Soft- bodied 

 I (but usually pro- 

 tected by a shell) 



Back boned 



Ex. Moneron, amceba, sponge 



Ex. Polyp, anemone, coral- 

 boilder 



Ex. Sea-urchin, starfish 

 Ex. Worm, crab, spider, ant 



Ex. Sea-squirt, oyster, snail, 

 cuttle-fish 



Ex. Fish and all other higher 

 life-forms to man 



are intimate and indissoluble, the several sub-kingdoms 

 merging one into the other like the colours of the rainbow. 

 Moreover, any consecutive arn\ngement cau only broadly 

 indicate the relative order of the several life-forms, because 

 development has not proceeded in direct line— eg", the ant, 

 which belong.s to the Annulosa, is the highest of all inverte- 

 brates ; but it is not, therefore, most nearly allied to the 

 lowest vertebrate. The connecting link between these two 

 great divisions, as will be shown presently, is found in the 

 double-necked, bottle-shaped sea-squirt, or AscidLin (Gr. 

 askidion, a little bottle), which is classed under the Mollusca, 

 and for this reason that sub- kingdom is placed last but one 

 in the ascending scale. If we go back far enough we find 

 the common starting-point of all, whence they travelled for 

 a while along the same road, and then diverged wider and 

 wider apart, until it now seems difficult to believe that the 

 lowest and highest of both plant and animal are one in 

 community of origin. 



I. Protozoa. — The lowest member of this group — in 

 other words, the lowest known animal, if we except certain 

 parasites, is the moneron (Gr. monos, single). Like the 

 lowest plants, it lives in water, the element in wliich life 

 had beginnings. It is an extremely minute, shapeless, 

 colourless, slimy mass, alike all over, and therefore without 

 any organs. When we say that it is alike all over, we 

 mean that our range of vision does not enable us to report 

 otherwise, for doubtless the simplest and smallest living 

 thing is very complex in structure. And we mean, 

 further, that there is no differentiation, as it is called — 

 i.e. no formation of specific oigans for the performance of 

 specific functions. The functions of living things are three- 

 fold — nutrition, reproduction, and relation ; in other words, 

 to feed, to multiply, to respond to the outer world, and all 

 these the organless moneron discharges. Every part of it 

 does everything : it takes in food and oxygen anywhere, 

 and digests and breathes all over its body. It literally 

 " gets out.side " its food, having the power of throwing out 

 finger-like prolongations, c;\lled pseudopods, or false feet, 

 with which it propels itself and spreads over its prey, 

 sucking the soft body even from shelly creatures and 

 casting away the refuse. So far as the function of 

 nutrition, which includes digestion, circulation, and rejec- 

 tion of wa.ste, and the function of reproduction, are con- 

 cerned, the moneron performs these as completely as the 

 highest animals. For these, with their complex sets of 

 oi^ns — lungs, heart, stomach, etc. — cannot do more than 

 nourish themselves and keep the body in health. And in 

 reproduction, which the moneron effects by dividing itself 

 into two, as do the lowest plants, wherein, as in it, there is 

 neither male nor female, it accomplishes in simple fashion 

 what the higher hfe forms can do only in a more complex 

 way. So that the difference — which, however, is in degree 

 and not in kind — between this slime-speck of protoplasm 

 and the higher organisms, all made of like stuff, is in the 

 discharge of the function of relation. 



Reference has been made to the response to stimulus from 

 external things manifested by the lowest life-forms although 

 there is no trace of a nervous system in them, and now that 

 we are treating of a living mass that not only feeds and 

 digests and breathes all over, but likewise feels all over, a 

 few remarks upon the origin of nerves may supersede the 

 need for an}' detailed account of the several nervous systems 

 in the represenUitive animal types. 



The function of the nerves is to bring the organism into 

 relation with its surroundings ; they are the special media 

 of communication between the body and the external world, 

 and between the brain and every movement of the parts of 

 the body. Starting in the higher animals from the encased 

 brain and ensheathed spinal cord, and diffused in the lower 

 animals in less complex arrangement, they report from 

 without to within. The vibrations of the ethereal medium 

 that afiect us as light enter the eye and pass along the 

 optic nerve, which conveys the impulse to the brain, and it 

 is the brain, not the eye, that sees. So with the air- 

 vibrations that travel along the aural nerves ; the sensation 

 of sound resides in the brain, not in the ear ; so with all 

 the manifold sensations that we feel. 



Thereft)re, wher-ever there is sensitiveness to impressions, 

 however dim and feeble this may be, there the function of 

 relation is being exercised. This sensitiveness is exhibited 

 by the moneron in its shi'inking when touched, and in its 

 grip of food ; but the sensitiveness is diffused, and not 

 located in anj' organs. In members of the .<ame sub- 

 kingdom as it, there are faint traces of approach to nerve- 

 structure, and the development of this is manifest in 

 ascending scale tUl in the highest life-forms, among certain 

 invertebrates and vertebrates, it i caches subtlest com- 

 plexity. 



Now as every part of a living thing is made up of cells, 

 and the functions govern the form of the cells, the origin of 

 nerves must be due to a modification in cell shape and 

 arrangement, whereby certain tracts or fibres of com- 

 munication between the body and its >urroundings are 

 originated. 



But what excited this modification ? The all-surround- 

 ing medium, without which no life had been, which deter- 

 mined its forms and limits, and touches it at every point 

 with its throbs and vibrations. In the beginnings of a 

 primitive layer or skin exhibited by creatures a stage above 

 the moneron, unlikenes.ses would arise, and certain parts 

 would by reason of then- finer structure be the more readily 

 stimulated by, and the more quickly responsive to, the 

 ceaseless action of the surroundings, the result being that 

 an extra sensitiveness along the lines of least resistance 

 would be fet up in those more delicate parts. These, 

 developing, like all things else, by use, would become more 

 and more the selected paths of the impulses, leading, as the 

 molecular waves thrilled them, to structural changes or 

 modification into nerve-cells and nerve-fibres of ever- 

 increasing complexit}' as we ascend the scale of life. In 

 brief, the stimulated film becomes modified into filaments ; 

 and the entu-e nervous system, with its connexions : brain 

 and all the subtle mechanism with which it controls the 

 body ; organs of sense, with their mysterious selective 

 power — the eye to receive light-vibrations, the ear to 

 receive sound-vibrations, the nose to detect the fragrant 

 and the foul ; alike had their origin in infolded tracts 

 of the primitive outer skin. The brain arose from 

 such infoldings sinking down beneath the surface, and 

 finally becoming imbedded in other tissues ; the eye and 

 the ear, as their parts developed, were joined from 

 ■within by outgrowths from the brain. Such, in fewest 

 words, is that theorj* of the origin of nerve-s which, formu- 

 lated by Herbert Spencer, has been confirmed by all recent 



