February 1, 1887.] 



♦ KNOWLEDGE ♦ 



75 



Allen's position lies in this, that mewing life as a product of 

 Poicer operating under its separating action of Energy upon 

 Matter, an energy-storing organism must have come first. 

 If the firet protoplasm lacked chlorophyll, it had within it 

 the possibilities which permitted its secretion at an early 

 stage ; it was, to use an unavoidably long word, chloro- 

 phyllaceous. The question, however, is of no serious import- 

 ance in view of the common evolution of living things, and 

 we may pass to less debatable giound in inquu-y into the 

 ' causes which have developed them in countless variety from 

 specks'of relatively formkss protoplasm. 



The. cell .is the structural starting point of all life. It is 

 a small body of sticky consistence, enclosing a nucleus, 

 which ■ is the result of the first visible approach of proto- 

 plasm to unlikeness of parts, and the chief centre of activity. 

 Every cell arises by separation from a pre-exLsting cell, ami 

 every living organism is made up of one cell or of many 

 cells. The single cell of which the lowest organisms are 

 composed does everything appertaining to life : it feels, 

 moves, feeds, and multiplies. In the complex or many-celled 

 organisms these functions are divided among the cells, each 

 of which is independent, but nevertheless adapts itself for 

 the work it has to do. Division of laljour causes difter- 

 ence of structure ; stem, root, sap, leaf, and seed in the 

 plant ; bone, muscle, nerve-tissue, blood, and egg in the 

 animal ; all are communities of cells of astounding minute- 

 ness variously modified. 



The one-celled forms increase by division. Growth is the 

 balance of repair over waste, and when through assimilation 

 of food into its substance the cell reaches a certain size, the 

 force of cohesion is overcome by the release of the energy 

 derived from food, and the cell divides equally at the kernel 

 or nucleus. The slimy protoplasm disti'ibutes itself around 

 each nucleus as the two part company, to grow and divide 

 again in like manner ad injinilum. To these lowest Pro- 

 tozoa we may a])ply the words, " thou art the same, and thy 

 years shall have no end," at least till all Ufe here has end ; 

 for they were the Alpha, and may be the Omega, in the 

 earth's life-history ; neither is one before nor after the 

 other, since there is no descent amongst them, but only 

 latei-al multiplication. In many Protozoa a small portion of 

 the parent is detached, a process known as generation by 

 budding ; but this and other modes of whole or partial 

 fission are classed together as reproduction by multipli- 

 cation. 



The next stage in structure is when the cells, in dividing, 

 remain grouped together. In the plant, as has been shown 

 already, the secretion of an envelope of cellulose round each 

 cell, and the close union of the outer cells into a thick wall 

 which gives stability to the structure and protection to the 

 inner cells, causes the plant to lose touch, as it were, with 

 the outer world, compared with the less rigid surface of the 

 animal cells, which remained responsive in every part to 

 stimuli from without. 



The study of cell-division is profoundly intere.sting. The 

 cells divide in definite order into two, then into four, then 

 into eight, and so on, clustering together in a mulbeiry-like 

 mass. Mutual pressure of the surface-cells against one 

 another causes them to flatten into a membi-anous layer 

 covering larger and denser cells. At a later stage these 

 also spread out, the two layers forming the material out 

 of which are developed the most complex animals. These 

 layei-s, or cell-strata, which have been traced back to the 

 first stage of division of the germ or egg, compose the double 

 wall of the body of all animals above the Protozoa ; but 

 as we rise in the scale a third layer, larger and moi-e 

 complex, appears, from the subdivision of which the greater 

 number of organs of the body, be it of a worm or a man, are 

 developed. The upper layer gives rise to the skin, the 



nervous system, and organs of sense ; the lower layer to the 

 intestinal canal and appendages ; and the middle layere to 

 the general skeleton, the heart, and other important organs. 

 The animal kingdom, treating it broadly, has therefore a 

 threefold division — (1) simple forms, having no body cavity; 

 (2) intermediate forms, having body cavity; (3) highest 

 forms, having digestive caNaty sepamte from body cavity. 

 All have developed by slow and numberlass modifications 

 from the nucleus of a single cell, the higher passing through 

 the grades of structure of the lower in their growth from 

 the egg. 



All plants and animals above the lowest are reproduced 

 by the agency of special cells, the impregnation of the 

 nucleus of the germ or egg-cell of the female Ijy the nucleus 

 of the sperm-cell of the male being necessary. There are 

 numerous variations in the organs, but whatever unlike- 

 nesses exist in detail do not aflfect this general statement ; 

 alga and oak, sponge and man, are alike developed from 

 germs variously called spores, sacs, seeds, and eggs. The 

 structure of the egg of the parent determines the structure 

 of the offspring, which, as wDl be shown in due course, 

 reproduces the series of forms through which its ancestors 

 passed as it progresses to its adidt state. In other words, 

 the individual, as it developea from the egg-cell, epitomises 

 the history of its species. 



The transmission of parental form and structure, as well 

 as of mental character, to offspring, being clear, the question 

 suggests itself — How have variations, resulting in millions 

 of past and present species of plants and animals, arisen ? 



The ultimate causes of variations are extremely obsciure, 

 and possibly lie beyond human power to discover, but when 

 we consider the mobility and minute complexity of structure 

 of living things invisible to the naked eye, and their 

 response to every shiver of energy from without, we have 

 sufficing factors to produce unstableness which will result in 

 unUkeness of parts. Given a body which, although a minute 

 speck, contains billions of molecules performing complicated 

 movements of immense rapidity, and sensitive in incon- 

 ceivable degi'eo to the play of vibrations impinging upon 

 them at the i-ate of hundreds of trillions per second, would 

 not the marvel be if these quivering particles of the 

 structuie, shaken by energies within, and by still more 

 potent energies without, did not undergo continuous 

 redistribution ] 



The position may be thus stated. The organism has — 

 (1) Infinite complexity of structure; (2) Inherited tendencies ; 

 (3) Mobility and continuous motion, therefore tendency to 

 vary ; (4) Variations are induced by the surroundings on 

 which, as vehicles of energy, life depends ; (5) The sur- 

 roundings change, and the organism adapts itself or not to 

 the change ; (6) Such as fail to do this perish ; (7) Such 

 as adapt themselves vary in greater or lesser degree ; 

 (8) These variations, being transmitted, are stages in the 

 development of different life-forms. To put the matter 

 briefly — likenesses are inherited, variations are acquired. 



This brings us to the theory Hnked with Mr. Darwin's 

 name, and which explains by what operation of natuiul 

 causes the highest plants and animals have descended by 

 true generation and slow modification from less complex 

 life-forms, and these in ever-lessening degrees of complexity 

 and unlikeness until the common starting-point from the 

 lowest or one-celled organism is reached. 



Following Lyell's method of explaining the past by 

 agencies still in working, and adapting hints from Malthus 

 and other writers in the clearing up of questions suggested 

 by observations extending over many years, Darwin pro- 

 pounded a theory which, in the judgment of every biologist 

 unfettered by predilections or prejudices, accounts in large 

 degree for the origin of species. 



