January io, 1901] 



NATURE 



263 



reasonable, therefore, when we know these rays and skates to 

 have been derived from heavy-tailed shark-like ancestors with 

 small side-fins, than the question how far conversion of the tail 

 into an organ of electrical discharge may not have been the out- 

 come of the taking-on by the side-fins of the swimming function ? 

 The answer to this is convincing and complete, for we find 

 among the tropical and more distant allies of these rays, that the 

 tail may become by elongation in one species a delicate trailing 

 whip-lash ; by abbreviation in another a mere vestigial stump, 

 or by the addition of spines in yet another a formidable weapon 

 of offence. Clearly, rid of the propelling function, it has become 

 free to modify its ways, and the conversion into an organ of 

 electrical discharge is found to be but one of a series of 

 independent adaptations by "substitution." 



Other and more beautiful examples of the working of this law 

 might be cited, such, for example, as that of the provision for 

 " casting " the tail, so well known among living lizards ; but 

 sufficient is before us to show in what manner the advance of 

 knowledge dispels our difficulties, and that the stumbling-block 

 of one generation may become the stepping-stone of the next. 



If evolution — defined as the law of descent with modification, 

 and involving the process of progressive advancement and pas- 

 sage with time from the simple to the more complex— is all 

 sufficient to explain the existence and succession of the diverse 

 forms of life, it might well appear that the conditions of modifi- 

 cation are more complex and less regular than would have been 

 expected ; and we are, therefore, led to inquire in what the 

 determining cause of modification and hereditary tendency may 

 perchance consist. Looking back on the history of biology, 

 three great names stand out above all others as those of the 

 pioneers in its turning-points, Linne, Cuvier and Darwin. 

 Linne taught us how to name and describe the objects in nature ; 

 Cuvier impressed upon us the fact that unity of structure under- 

 lies the great diversity in superficial form ; Darwin, for the first 

 time, furnished the clue to this unity, on the lines to which I 

 have already referred, and showed us that vital phenomena are 

 attributable to the working of a fixed set of laws. 



It may be said of all living things that, so far 'as their bodies 

 consist of a mass of living substance, which we term protoplasm, 

 they are structurally identical. In seeking to classify them, be 

 they plants or animals, the sharpest working distinction to be 

 drawn is between those which consist of one structural unit or 

 are unicellular, and those which consist of an aggregate of units 

 or are multicellular — hence our terms Protozoa and Metazoa, 

 Protophyta and Metaphyta, or collectively Monoplastids and 

 Polyplastids, the term " plastid " being sometimes substituted 

 for "cell." While the monoplastids, mostly though by no 

 means all visible only under a lens, consist each of but one 

 cell, one structural unit, of the order of those which in the 

 aggregate compose the body of the polyplastid, there is no 

 fundamental difference recognisable in the manner and extent 

 to which multi- and uni-cellular beings stand related to the 

 universe at large. Both are motile and sensitive ; both pro- 

 duce waste, by processes which unchecked lead to decom- 

 position and death ; both stand, therefore, in need of recom- 

 position and must be nourished ; and both are loyal to the 

 divine command to increase and multiply. It is concerning 

 this reproductive process that the post-Darwinian period has 

 witnessed an altogether unparalleled activity, in the attempt to 

 get at the essence and to unravel the mystery of hereditary 

 influence. The mental giant who has led the way is Prof. 

 Weismann, of the University of Freiburg, in Breisgau. 

 His whole series of doctrines find their focus in three epoch- 

 marking addresses, which he delivered in 1881-1883 before the 

 Association of German Naiuralists and his University, en- 

 titled " On the Duration of Life," " On Heredity" and " On 

 Life and Death." He took his stand upon the well-known 

 fact that whereas reproduction of the unicellular organism is by 

 a simple process of fission, the individual dividing into two 

 without loi-s of substance, and becoming at once parent and off- 

 spring—in the multicellular organism the reproductive act in- 

 volves only an insignificant portion of the body, and is sooner 

 or later accompanied by the death of that which remains, and a 

 consequent loss of substance. From this he argued that inas- 

 much as it is conceivable that the fissiparous process may go on 

 indefiniiely, the Protozoan of to-day may have arisen by repeated 

 and prolonged fissiparous activity from that of long passed ages, 

 and that the organism, never having suffered a loss of substance, 

 may be immortal. Founding, in this way, his doctrine of the 

 " Immortality of the Protozoa," he was led, by realisation that 



NO. 1628, VOL. 63] 



that portion of the body of the multicellular organism which 

 fulfils the reproductive function passes to its share in the forma- 

 tion of a new individual a living element, to distinguish between 

 it, the " germ-plasma " which never dies, and the rest of the 

 body or " somatoplasma," which is lost by decomposition and 

 death, and he in this way sought to extend the conception of 

 immortality to the reproductive elements of the higher organisms. 



This marvellous generalisation — prettier far than poetry — 

 created in the early " nineties " a veritable furore ; and it 

 furnishes us with material for reflection and mental consideration 

 of an altogether unique order. So profound, however, was its 

 effect upon contemporary science and thought, that under its 

 influence there arose a horde of eager investigators, intent on its 

 development and the search for the seat of primary hereditary 

 influence. The literature and vexed controversies which have 

 in consequence arisen are now voluminous, and Weismann and 

 his followers, eager to push forward, have pressed theory upon 

 theory, often with contradictory effect. His whole series of 

 observations, however, focus in the afore-named great generali- 

 sation, and, as for alleged contradiction, I can only regard it as 

 due to the influence of his friends, who, eager for his advance, 

 and perhaps, in the case of some, for association with his work, 

 forced him to extremes which he would never have contemplated 

 had he been left alone. 



As might be supposed, the conception of the immortality of 

 protoplasm has not passed unchallenged. Maupas, an acute 

 French investigator, has discovered of the familiar " Bell 

 Animalcules," that prolonged fissiparous reproduction is accom- 

 panied by progressive diminution in stature, leadin , if un- 

 checked, to senility and decay ; and, having determined by ob- 

 servation the number of generations in which this veritable 

 extinction may be brought about, he has succeeded in proving 

 that, by means of a conjugative process, involving a blending of 

 two individuals, its effects are overcome. To what this remark- 

 able discovery may ultimately lead we know not, but it so 

 happens that, whether the conception of immortality be right or 

 wrong, it arose in the minds of trained naturalists long before 

 Weismann's time. He himself starts with a quotation from 

 Johannes Midler, the founder of comparative anatomy, to the 

 effect that " organic bodies are perishable, and that, while life 

 maintains the appearance of immortality, in the constant succes- 

 sion of similar individuals, the individuals themselves pass away." 

 And similarly, R. Owen, in two great lectures on " Partheno- 

 genesis," delivered before the Royal College of Surgeons, in 

 1849, came nearer the mark, with the astounding paragraphs : — 



" Not all the progeny of the primary germ-cell are required 

 for the formation of the body of all animals ; certain of the 

 derivative gerni-cells may remain unchanged, and become in- 

 cluded in that body which has been composed of their metamor- 

 phosed and diversely combined or confluent brethren. So 

 included, any derivative germ-cell .... may commence and 

 repeat the same processes of growth and imbibition, and of pro- 

 pagation by spontaneous fission, as those to which itself owed its 

 origin, followed by metamorphoses and combinations of the 

 germ-masses so produced, which concur to the development of 

 another individual, and this may be, or may not be, like that 

 individual in which the secondary germ-cell or germ-mass was 

 included." 



And, concerning the conception of immortality of the Proto- 

 zoa, he also wrote : — 



" It is by no means easy to find a name for the relation in 

 which the fissiparous monad stands to the two monads between 

 which it has been equally divided. A parent retains its individ- 

 uality distinct from its progeny ; but the monad has become a 

 part, and indeed the chief part, of the two that have resulted 

 from its spontaneous fission. Both separate moieties are, in 

 an equal degree, the same individual as the whole from which 

 they proceeded ; and in an infinitesimal, though conceivable, de- 

 gree, the actual monad is the same individual as the first created 

 one, from which it may have proceeded by an uninterrupted 

 succession of spontaneous fissions, and in that degree it may be 

 viewed as one of the oldest known individuals in creation, the 

 individual being never wholly or in part deceased." 



Not that this in any way detracts from the merits of Weis- 

 mann's labours ! On the contrary, to him is due the credit of 

 having put the vitally important topic which now concerns us on 

 a scientifically sound and workable basis — an achievement of 

 which he may well be proud. 



It being evident that the unicellular and multicellular organ- 

 isms stand alike responsible to the universe at large concerning 



