June 15, 1900.] 



SCIENCE. 



925 



the life of the individuals produced by the 

 affected reproductive organ ? I can give no 

 answer to this question. We have no data 

 upon which to form a judgment. We can- 

 not say whether it is possible permanently 

 to modify the constitution of an organism 

 in this way, or whether, however strong the 

 cause may be, consistently of course with 

 the non-destruction of life, the effects wiU 

 gradually die away — it may be in one, it 

 may be in two qr more generations. There 

 are cases known which might assist in 

 settling these questions, but I must leave 

 to another opportunity the task of examin- 

 ing them. I refer to such cases as Artemia 

 salina, various cases of bud variation which 

 cannot be included under the head of growth 

 variation. 



SENILE DECAY AND EEJUVENESOENCE OF 

 ORGANISMS. 



Another question, also of the utmost im- 

 portance, confronts us at this point. As is 

 well known, organisms are liable to wear 

 and tear, sooner or later some part or parts 

 essential to the maintenance of the vital 

 functions wear out and are not renewed by 

 the reparative processes which are supposed 

 to be continually taking place in the organ- 

 ism. This constitutes what we call senile 

 decay, and leads to the death of the organ- 

 ism. As a good example of the kind of 

 cause of senile decay, we may mention the 

 wearing out of the teeth, which in mammals 

 at any rate are not replaced ; the wearing 

 out of the elastic tissue of the arterial wall, 

 which is probably not replaced. There is 

 no reason to suppose that the reparative 

 process of any organism is sufficienbly com- 

 plete to prevent senile decay. There is 

 probably always some part or parts which 

 cannot be renewed, even in the simplest 

 organisms. Maupas has shown that this 

 holds for the ciliated Infusoria, and he has 

 also shown how the renewal of life, which 

 of course must be effected if the species is 



to continue, is brought about. He has 

 shown that it is brought about by conjuga- 

 tion, during which process the organism 

 may be said to be put into the melting-pot 

 and reconstituted. For instance, many of 

 the parts of the conjugating individuals are 

 renewed, including the whole nuclear ap- 

 paratus, which there is every reason to be- 

 lieve is of the greatest importance to living 

 matter. 



On reconsidering the life of the Metazoa 

 in light of the facts established by Maupas 

 for the Infusoria, we see that all Metazoa 

 are in a continual state of fission, as are the 

 ciliated Infusoria. They are continually 

 dividing into two unequal parts, one of 

 which we call the parent and the other the 

 gamete. The parent Metazoon must event- 

 ually die ; it cannot be put into the melt- 

 ing-pot; its parts cannot be completely 

 renovated. The gamete can be put into 

 the melting-pot of conjugation, and give 

 rise to an entirely reconstituted organism, 

 with all the parts and organs brand new 

 and able to last for a certain time, which is 

 the length of life of the individual of the 

 species. 



Is there any other way than that of con- 

 jugation by which an organism can acquire 

 a complete renewal of its organs? Is the 

 renewal furnished by the development of 

 all the parts afresh which takes place in a 

 parthenogenetic ovum such a complete re- 

 newal ? This question cannot now be cer- 

 tainly answered, but the balance of evidence 

 is in favor of a negative answer. And this 

 view of the matter is borne out by a con- 

 sideration of the facts of the case. In all 

 cases of conjugation which have been thor- 

 oughly investigated, the nuclear apparatus 

 is completely renewed. It would appear in- 

 deed as though the real explanation of the 

 uninuclear character of theMetazoon gamete 

 is to be sought in the necessity of getting 

 the nuclear apparatus into the simplest 

 possible form for renewal. N"ow in the de- 



