926 



SCIENCE. 



[N. S. Vol. XI. No. 285. 



velopment of a parthenogenetic ovum the 

 ordinary process of renewal of the nucleus 

 is often in partial abeyance. As a rule it 

 only divides once instead of twice, and 

 there is, of course, no reinforcement by nu- 

 clear fusion. It is, of course, possible that 

 the reinforcement by nuclear fusion which 

 occurs in conjugation may have a different 

 explanation from the nuclear reconstitution 

 which takes place in the formation of polar 

 bodies and similar structures. On the other 

 hand, it may all be part of the same process. 

 "We cannot tell. So that we are unable to 

 answer the question whether for complete 

 rejuvenescence a new formation of all parts 

 of the organism is sufficient, or whether a 

 reconstitution of the nuclear apparatus of 

 the kind which takes place in the matura- 

 tion of the Metazoon ovum and the division 

 of the micro-nucleus of Paramecium is also 

 required ; or finally, whether in addition to 

 the latter phenomenon a reinforcement and 

 reconstitution by fusing with another nu- 

 cleus is also necessary for that complete 

 rejuvenescence which enables an organism 

 to begin the life cycle again and to pass 

 through it completely. 



"With regard to buds in plants there is 

 reason to believe that they share in the 

 growing old of the parent. That is to say, 

 if we suppose the average life of the indi- 

 vidual to be 100 years, a bud removed at 

 50 will be 50 years of age, and only be able 

 to live on the graft for 50 more years. 



HEEEDITT. 



Having now spoken at some length of the 

 phenomenon of variation, I must proceed 

 to consider from the same general point of 

 view the phenomenon of heredity. 



As we have seen, in asexual reproduction 

 heredity appears, as a general rule, if not 

 always, to be complete. The offspring do 

 not merely present resemblances to the pa- 

 rent — they are identical with it. And this 

 fact does not appear to be astonishing when 



we consider the real nature of the process. 

 Asexual reproduction consists in the sepa- 

 ration off of a portion of the parent, which, 

 like the parent, is endowed with the power 

 of growth. In virtue of this property it 

 will assume, if it does not already possess 

 it, and if the conditions are approximately 

 similar, the exact form of the parent. It 

 is a portion of the parent; it is endowed 

 with the same property of growth; the 

 wonder would be if it assumed any other 

 form than that of the parent. Indeed, it is 

 doubtful if the word heredity would ever 

 have been invented if the only form of 

 increase of organisms was the asexual one, 

 because there being no variation to contrast 

 with it, it would not have struck us as a 

 quality needing a name, any more than we 

 have a name for that property of the num- 

 ber two which causes it to make foitr when 

 duplicated. 



The need for the word heredity only be- 

 comes apparent when we consider that 

 other form of reproduction in which the 

 real act of reproduction is associated with 

 the act of conjugation. Looking at repro- 

 duction from a broad point of view, we 

 may sum up the difference between the two 

 kinds, the sexual and the asexual, by say- 

 ing that whereas the essence of sexual re- 

 production is the formation of a new indi- 

 viduality, asexual reproduction merely con- 

 sists in increasing the number of one kind 

 of individual. From this point of view 

 sexual reproduction is better termed the 

 creation of a new individuality, for that, 

 and not the increase in the number of indi- 

 viduals, is its real result. Inasmuch as 

 conjugation of two organisms is the essen- 

 tial feature of sexual reproduction, it would 

 appear that the number of individuals would 

 be actually diminished as a result of it ; 

 and this does really happen, though in a 

 masked manner, for we are not in the habit 

 of looking upon the spermatozoon and ovum 

 as individuals, though it is absurd not to 



