128 



SCIEN'CE. 



[Vol. VIII , No. 183 



fresh insight into the morphological basis, but also 

 into the physiological function of heredity. 



A few words are necessary about pangenesis. 

 The hypothesis, as originally advanced by Darwin, 

 was the suggestion of a masterly mind, and as a 

 succinct and comprehensive expression of the facts 

 of heredity, commands admiration. But the real 

 worth and real significance of the hypothesis have 

 not been grasped by those who have tried to bet- 

 ter it : its value was not in explaining, but in 

 expressing, heredity in hypothetical terms, which 

 were at once suggestive and comprehensible. 

 Haeckel, whose judgment has too often to be de- 

 plored, accepted pangenesis in the mistaken way, 

 and made an attempt to improve upon it as an 

 explanation, in a pamphlet ^^ which no competent 

 critic any longer assigns serious value to. Indeed, 

 were some one to assert that the alliterative 

 euphoay of its title, ' Die perigenesis der plasti- 

 dule,' was its cleverest part, a physiologist might 

 feel unable to prove the assertion erroneous. Ac- 

 cording to Darwin's hypothesis, every part of the 

 body throws off particles, or gemmules, and some 

 of these from each portion of the body enter the 

 sexual elements, each of which, therefore, con- 

 tains contributions from every part of the parent. 

 The gemmules, by their multiplication in the 

 embryo, reproduce their own kind, and so rebuild 

 on the foruier pattern. Haeckel's perigenesis is, 

 when separated from his rhetoric, the substitution 

 of rhythmical vibrations for the different kinds 

 of gemmules. It need hardly be said that not a 

 tittle of evidence for this notion is shown, and 

 that, as elaborated by its author, it violates the 

 elementai'y laws alike of biology and physics. In 

 these respects it recalls the delightful theory of 

 Dr. Cohen," who, having noticed a certain re- 

 semblance of the ovum to a ganglion cell of the 

 spinal cord, and of the spermatozoon to the 

 unipolar cells of the sympathetic ganglia, gravely 

 concludes, " The influence of the spermatozoon, 

 the male hereditary influence, extends above all to 

 the cerebro-spinal system, while the action of the 

 ovulum, Goethe's 'ewig weibliches,' shows itself 

 above all upon the organs subordinate to the sym- 

 pathetic nervous system " (pp. 30-31). In physics, 



18 The pamphletwas published at Berlin in 1876. For some, 

 considering its character, very gentle criticisms, see Ray 

 Lankester in Nature, July 13, 187(), xiv ^35-238. Elsberg has 

 also written on the subject in the Proc . Amer. assoc. adv. sc, 

 XXV. 178, and cites there earlier writings of his own. The 

 perusal of his article has not enabled me to recognize any 

 thing novel except the substitution of the term ' plastidule,' 

 for 'gemmule ' used by Darwin, and speculations as to com- 

 position of plastidules, as if he was groping after the eou- 

 ception of the micella of Nageli, with which he was ap- 

 parently unacquainted. 



" Das gesetz der befruchtung und vererbung, etc., 

 Nordlingen, 1875. 



also, Cohen even surpasses Haeckel : he attributes 

 (p. 19) the entrance of the spermatozoon into the 

 ovum to reaction between the positive electricity 

 of the one and the negative of the other. 



Brooks's '« modification of the theory of pangen- 

 esis well deserves consideration, although the sub- 

 sequent progress of biology does not lead me to 

 think it felicitous ; but we can now recognize it as 

 a step towards Nussbaum's valuable theory, and 

 also towards Weismann's conception that sexual 

 reproduction has for its object the maintenance of 

 variability. Brooks's theory is advocated in his 

 book on ' Heredity ' (Baltimore, 1879) : he states 

 it succinctly ^^ as follows : — 



" This paper proposes a modification of Darwin's 

 hypothesis of the same name (pangenesis), remov- 

 ing most of its difficulties, but retaining all that is 

 valuable. According to the hypothesis in its mod- 

 ified form, characteristics which are constitutional 

 and already hereditary are transmitted by the 

 female organism by means of the ovum ; while 

 new variations are transmitted by gemmules, 

 which are thrown off by the varying physiological 

 units of the body, gathered up by the testicle, and 

 transmitted to the next generation by impregna- 

 tion." 



If this theory was tenable, there should be — to 

 mention a single objection — little variation in 

 individuals produced by parthenogenesis ; and they 

 ought always to be females, whereas they are 

 sometimes males. There remains, not a new 

 theory of pangenesis, but the valuable suggestion 

 that the maternal influence causes less variability 

 than the paternal. I am, however, strongly dis- 

 inclined to anticipate the confirmation of this 

 suggestion, especially because the males are not 

 more variable than the females, as we should 

 expect. I have some extensive statistics, which 

 show that in mammals, at least, there are no 

 essential differences between the sexes in variabil- 

 ity. Even if Brooks's thesis should be established, 

 it would prove only that the inheritance from the 

 mother is stronger than from the father, and there 

 would lack reasons for his abstruse hypothesis. 



The first important step towards the substitution 

 of a new theory, vice pangenesis, was taken by Dr. 

 Moritz Nussbaum, whose memoirs " on the differ- 

 entiation of sex deserve great attention. Every 

 one who feels interest in the general problems of 

 biology, and is able to follow a technical paper, 

 will find Nussbaum's memoirs profitable reading. 



18 Proc. Amer. assoc. sc, Buffalo, 187B, p. 177. abstract 

 of a paper read before the section of natural history. 



13 'Zur differenzirung des gescblechtes im thierreioh.,' 

 in Arch, fur mikrosk. anat., xviii. (1880) pp. 1-113; and 

 ' Feber die veranderung der geschlechtsprodukte bis zur 

 eifurchung, in Ibid., xxiii. 155. 



