198 



KNOWLEDGE. 



[August 1, 1890. 



leading objections wliicli tell in favour of the older 

 view. 



1. As against Prof. Weismann"s contention against the 

 rise of new species except through the agency of sexual 

 I'eproduetion, there are the numerous cases of a sexual 

 fungi which show no sign of extinction, one family, as 

 Prof. Vines points out, " of the most varied fonn and 

 habit, including hundreds of genera and species, in which, 

 so far as minute and long-continued investigation has 

 shown, there is not, and probably never has been, any 

 trace of a sexual process." ■■ And like evidence is supplied 

 by certain wheel-animalcules. 



2. So far as acquired muscular developments and muti- 

 lations are concerned, doubtless the e\-idence of their 

 transmission is of the slenderest kind. Generations of 

 dogs whose tails and ears have been docked have not pro- 

 duced puppies with corresponding mutilations ; the chil- 

 dren of one-eyed, one-armed, and one-legged parents are 

 born with their full complement of limbs and eyes, 

 nor is it proved that the offspring of blacksmiths and 

 navvies appear with abnormally developed biceps. But 

 although this may hold good of gross and non-vital parts, 

 Professor Weismann has a more difficult task in contend- 

 ing that it also does not apply to the subtle processes which 

 initiate changes in vital parts. Upon this it is far from 

 easy to get at his real meaning, for his statements are 

 "hedged " with qualifications. 



In his essay on " The 8igniiicance of Sexual Reproduc- 

 tion in the Theory of Natural Selection '* it is admitted 

 that " the ultimate origin of hereditary individual differ- 

 ences lies in the direct action of external influences upon 

 the organism."! "In what way," he asks, ; "could the 

 transformation of species be produced, if changes in the 

 germ -1)1 asm cannot be transmitted "' And how could 

 the germ-plasm be changed except by the operation of 

 external influences, using the words in their widest 

 sense '? " But immediately after the first of these ex- 1 

 tracts, he says, " Hereditary variability cannot, however, 

 arise in this way at every stage of organic development, 

 as biologists have hitherto been inclined to believe. It I 

 can only arise in the lowest unicellular organisms, and 

 when once individual difference had been attained by ' 

 these, it necessarily passed over into the higher organisms 

 when they first appeared." Turning back to the essay on I 

 " The Continuity of the Germ-Plasm," we read* as | 

 follows: — " I am also far from asserting that the germ- I 

 plasm is absolutely unchangeable or totally uninfluenced 

 by forces residing in the organism within which it is trans- 

 formed into germ-cells. I am also compelled to admit 

 that it is conceivable that organisms may exert a modify- 

 ing influence upon their germ-cells, and even that such a ! 

 process is, to a certain extent, inevitable. The nutrition I 

 and growth of the individual must exercise some influence 

 upon its germ-cells, but in the first place this influence ; 

 must be extremely slight, and in the second place it can- j 

 not act in the manner in which it is usually assumed that j 

 it takes place. "j The manner in which the influence acts 

 is a matter of observation which, h-om the nature of the 

 case, is beset with difficulty ; that the influence is slight 

 is of quite secondary importance, because, however small i 

 may be the effect, its repetition and accumulation through 

 generations will give us all the proof we need of trans- I 

 mission of functionally-acquired characters. Really, after i 

 such admissions on the part of Professor Weismann, there 

 seems little left to argue about, but for his arbitrary arrest 



* Nature, 2+ Oct. 1880, p. G26. 

 t Essinjs. p. 27S>. 

 t lh:d.. p. 411. 

 § Ibid.,Tf. 170. 



of the action of external influences in organisms above the 

 Protozoa. 



That these arc many -celled does not destroy the fact of 

 their fundamental unity, or make other than incredible 

 the theory that the germ-plasm can exist in the organs 

 of rei)roduction unchanged by the variations which modify, 

 more or less, the whole nduui. How is the theory of an 

 imaff'ected, insulated germ-plasm to be reconciled with 

 the ceaseless manufacture, secretion, and expulsion of 

 germ-cells which goes on through active life, the materials 

 of which are derived ft-ora the materials which nourish 

 the entire organism, the complexity of the cells of which 

 may, for aught we know, be as subtle as those of the 

 germ-cells ? And, moreover, how can that theory be 

 reconciled wuth the subtile influences of altered physical 

 conditions, and especially of the nervous system on the 

 reproductive system '? 



Besides this, there is a multitude of organisms in which 

 the germ-plasm is not located in one place, but dift'used 

 throughout. Any part of a Hi/ilni when cut oS' will grow 

 into an entire animal ; fresh plants, producing flowers and 

 fruit, will grow from the fragments of the leaves of the 

 Bei/oniii, and Professor Eimer cites the case of a forest of 

 young fronds which sjirouted from a thallus of Lunidiniit 

 vidi/aris which had been " cut up with a sharp knife on a 

 smooth plate of cork untU the fragments were so small as 

 to form a coarse-grained pulp,"* which was then spread 

 on moist sand. Such instances as these, to which the 

 famUar case of the propagation of the potato through the 

 tuber may be added, render it " difficult," as Sir W. 

 Turner remarks, " to understand why the nutritive pro- 

 cesses which affect and modify the soma-cells should not 

 also react upon the germ-plasm." 



3. Space forbids detailed reference to the striking ex- 

 periments of Hoffmann on wild flowers, in which double 

 flowers obtained by continuous cultivation from normal wild 

 flowers became hereditary, and to the observations of Yung 

 on change of sex of tadpoles by altering the nature and 

 quality of their food, ' and we must pass to what appears 

 the chief cnu- in Prof. Weismann's theory, namely, the 

 impossibility of reconciling psychological evolution with 

 the continuity of the germ-plasm. 



Among the most solid contributions which Mr. Spencer 

 has made to biology in its highest aspects is his theory of 

 the genesis of the nervous system, a theory which is con- 

 firmed by the observations of the lamented Francis Balfour 

 and other embryologists. That system, both in man and 

 the lower animals, had a common origin in modifications 

 of the primitive skin due to the direct action of the envi- 

 ronment. The irritability which characterizes the entire 

 surface of the lowest animals gradually became concen- 

 trated in definite tracks and led to the formation of nerve- 

 centres. " The functions of the central nervous system, 

 which were originally taken by the whole skin, became 

 located in a special part of the skin which was step by 

 step removed from the surface," * the brain itself " arising 

 from an infolded tract of the outer skin which, sinking 

 down beneath the surface, became imbedded m other 

 tissues and eventually surrounded by a bony case." j 

 Here, if anywhere, seems incontrovertible proof of the 

 origin of the structures through which we apprehend the 

 outer world in the play of that outer world upon the super- 

 ficial parts of the organism. " These structures,' as Mr. 

 Spencer says, "once commenced, and furthered by natural 



* Eimer, p, 395. 



t Jiiofiition of Sex, by Geddes and Thonison, p. 41. 

 X Spencer's factors of Organir Evolution, p. 66. 

 § Balfour's Treatise on Comparative Embryoloijy, vol. ii., p. 400 

 (Second Edition.) 



