196 



KNOWLEDGE 



[August 1, 1890. 



since 1881, abstracts of which by Professor Moseley and 

 otliers ha^•(' appeared from time to time iu Xatiire, and, 

 under the title of the " Transmission of Acquired 

 Characters," were the subject of an important debate 

 opened by Professor Ray Lankester at the Manchester 

 meeting ot the British Association in 1887, Professor 

 Weismauu taking part in tlie discussion. Witliin the last 

 few months the whole of Professor Weismann's essays 

 have been collected and issued by the Clarendon Press as 

 one of the volumes of the series of Foreign Biological 

 Memoirs, so that the English reader has now the oppor- 

 tunity of learning about the last deliverances on the 

 subject of " heredity and kindred problems " in his mother 

 tongue. The publication of this volume gave rise to an 

 able and, in fundamental points, adverse criticism by Sir 

 William Turner at the Newcastle meeting of the British 

 Association last autumn, and this has been followed by 

 the appearance of a translation of Professor Elmer's book" 

 on the same lines, as well as by Professor Vines's attack 

 in Xiiture, to which Professor Weismann has replied in that 

 journal, and by a voluminous correspondence which shows 

 no sign of yet coming to an end. So that a considerable 

 body of literature of the subject exists, and as the substance 

 of what Professor Weismann has said is in scattered form 

 not very easy to follow through the detached essays, an 

 attempt to focus and present it in untechnical form may 

 be of service. The learned Professor had asked himself, 

 as every thoughtful biologist pondering over the mystery 

 has asked : " How is it that a single microscopic cell, 

 imbedded in the ovum of the mother, can reproduce the 

 physical and mental features of the parents down to the 

 minutest details, and with these, not infrequently, certain 

 characteristics of grand-parents and of more remote 

 ancestors ? " 



Several converging lines of observation and thought led 

 him to the theory of the basis of heredity which is given 

 in the essays, and of these the two following are the main 

 tracks. Firstly, that death is not a primary attribute of 

 living matter. Secondly, that characters aajuired by the 

 parent are not transmitted to the ofi'spring. 



Pi'ofessor Weismann admits that the problem of the 

 origin of life remains unsolved, and probably is insoluble ; 

 we know that life had a beginning and that it will have an 

 end, but we know nothing more about it. The case is 

 dift'erent, however, in respect to death. There is a vast 

 number of living things which do not die naturally. Of 

 course they perish through various causes ; they are eaten, 

 or destroyed by accident, by intense heat and other 

 agencies. But so long as the normal conditions which 

 brought them into being remain ; so long as the conditions 

 necessary to their existence are fulfilled ; they neither 

 decay nor die, having within them the power of an endless 

 life. The organisms upon whom is thus laid no burden 

 of mortality, with such pangs of separation, and such dread 

 of the unknown, as are ours, lie at the very bottom of 

 the scale of life. All livings things are, for purposes of 

 convenience, divided into two classes : the Protozoa or 

 one-celled, and the Metazoa or many-celled. The one- 

 celled class includes the lowest and simplest forms, and 

 the many-celled includes all other organisms in unbroken 

 continuity of development, as, in animals, from sponges up 

 to men. 



Now it is the Protozoa which Professor Weismann says 

 arc alone immortal. Each Protozoon is a microscopic 



* Organic Evolution as the liesult of the Inheritance of Ac(juired 

 diameters accordini/ to the Lawn of Organic Growth. By Dr. 

 Theodor Eimer. Translated by J. T. Cunningham, M.A. (Jlacmillan 

 &Co., 1890.) 



mass of a jelly-like substance, seemingly structureless, 

 without apparent uulikeness or separation of parts. There 

 is in the very simplest no body-cavity, no trace of a nervous 

 system, but only a nucleus or minute particle near the 

 centre. Every part of this one-celled organism does 

 everything. Food and air are absorbed through the 

 general surface ; and locomotion through the water, in 

 which medium it lives, is efiected by pushing out finger- 

 like processes. Although under certain conditions, as of 

 drought or frost, it dries up, it resumes an active life when 

 favourable conditions return. It performs an arithmetical 

 feat in multiplying itself by division. The more it eats the 

 bigger it gets, tOl such disproportion between the mass 

 which needs food and the surface through which the food 

 is received is reached that it divides equally, at the nucleus, 

 into two parts. Each half becomes a complete individual, 

 and grows in like manner till it also divides ; and so on 

 with the multiplication of Protozoa ad iiifinituin. Now it 

 cannot be said of either half that one is parent and the 

 other offspring, for both are of the same age, and only in 

 a limited sense can we speak of succession of generations 

 as the sub-divisions into separate individuals are repeated. 

 Nor is there anything analogous to death in these pro- 

 cesses. "There are," Professor Weismann says, "no 

 grounds for the assumption that the two halves of an 

 amoeba are diS'erently constituted internally, so that, after 

 a time, one of them will die while the other continues to 

 live. Such an idea is disproved by a recently discovered 

 fact. It has been noticed in one of the foraminifera, and 

 in other animals of the same group, that when division is 

 almost complete, and the two halves are connected only 

 by a short strand, the protoplasm of both parts begins to 

 circulate, and for some time passes backwards and forwards 

 between the two halves. A complete mingling of the 

 whole substance of the animal, and a resulting identity in 

 the constitution of each half, is thus brought about before 

 the final separation. '"■= Of course, as Professor Weismann 

 points out elsewhere, ^ the immortality of one-celled organ- 

 isms and (as will be shown presently) of the germ-cells 

 of the Metazoa, is potential, not absolute. " It is not that 

 they must live for ever, as did the gods of the ancient 

 Greeks — Ares received a ' mortal wound ' and roared for 

 pain like to ten thousand bulls, but could not die — they 

 can die, the greater number in fact do die, but a propor- 

 tion lives on which is of one and the same substance with 

 the others." An immortal, unalterable living substance 

 does not exist, but only immortal forms of activity of 

 organised matter. 



Now, as the Metazoa are descended from the Protozoa, 

 one is curious to learn how Professor Weismann explains 

 the evolution of the mortal from the immortal, because, as 

 we shall see, the many-celled have "put on mortality." 

 He accounts for this by " unequal fission," in other words, 

 the failure of certain one-celled organisms to divide them- 

 selves completely, whereby unlikeuess of parts and differ- 

 ences of position of parts resulted. " The first multi- 

 cellular organism was probably a cluster of similar cells, 

 but these imits soon lost the original homogeneity. As the 

 result of mere relative position there arose division of 

 labour, some of the cells were especially fitted to provide 

 for the nutrition of the colony, while others undertook the 

 work of reproduction." ; Obviously, those on the outside, 

 being exposed to the direct and constant action of their 

 surroundings, would be the media of nutrition, and be 

 builders-up of the cell-commonwealth. So the result of 



* Kssai/s on Heredity, ^-c. p. 26. 

 t Nature, 6 Feb. 1890," p. 318. 

 t Essays, p. 27. 



