564 SUMMARY OF CURRENT RKSEARCHES RELATING TO 



there is often no death of the persona till sexual reproduction occurs. 

 The persona] form may disappear periodically, but this can be evaded 

 artificially. 



Death from old age is very general ; it is abetted by the voracity of 

 other organisms, by parasitic and other diseases, by environmental 

 vicissitudes, by scarcity of food. In fishes the vast majority die young 

 — of hunger, external vicissitudes, and disease. Death at the hands of 

 other organisms is much less general than is usually supposed. Natural 

 death — as distinguished from violent death, or death due to parasites 

 and microbes — may be brought about by lack of nutrition, accumulation 

 of poisonous waste products in the medium, and by the arrears of wear 

 and tear. The first two are not so fundamental as the third, which is 

 primary. The hypothesis is advanced that there is with growing age an 

 accumulation of waste-products, which may become particularly asso- 

 ciated with the solid substances of the nucleus. Various waste-products 

 — the dross of the combustion — encumber the organism as age goes on, 

 though they are often effectively dealt with. 



The function of the nucleus is discussed at length, especially as 

 regards the cell-ferments. The nucleus collects these and modifies them 

 and returns them to the cytoplasm. Great importance is attached to 

 the granules or chromioles in the chromatin bands, which divide severally 

 into two and are equally distributed to the daughter-cells. The chro- 

 mioles are the chief vehicles of the hereditary primordia. 



In regard to heredity a sharp distinction is drawn between the 

 inheritance of type, for which the organization of the cytoplasm is very 

 important, and personal inheritance, which altogether depends on the 

 nucleus. The chromioles which bear the hereditary qualities must be 

 thought of as having definite structural organization, as distinguished 

 from ferments. The new person that arises in cross-fertilization has its 

 structural basis in the chromioles. 



Rejuvenescence has for its chief role the avoidance or removal of 

 waste-products in the nucleus. It may occur apart from sexual repro- 

 duction, e.g. by elimination of parts of the nucleus and a change in the 

 metabolism. It occurs in sexual reproduction in the giving off of polar 

 bodies, in the change in the composition of the zygote, and in changes 

 of metabolism. In fertilization there should be distinguished : (1) the 

 stimulus to development ; (2) the formation of a new person ; and 

 (3) rejuvenescence. The author concludes his essay with a discussion 

 of Mendelism, inbreeding, selection, mutation, and the origin of species. 



b. Histology. 



The Evolution of the Cell.*— The late Prof. E. A. Alinchin 

 emphasized the idea of the cell as a complete organism, whether main- 

 taining itself singly and independently, or in union with other similar 

 but individually specialized cells. He could not, however, regard the 

 cell in multicellular organisms as anything like the primordial unit or 

 starting-point in the evolution of organisms. It is necessary to study 

 the Protista to find relatively simple forms. In some of these the 



* Pres. Address, Section D, Brit. Assoc, 1915, pp. 1-28. 



