SOME PROBLEMS OF REPRODUCTION. 65 
ago. The one case which occurs to me, writing in Ireland, 
is the Champion Potato, which proved the salvation of the 
country after the great famine by its resistance to the 
“blight ” (Phytophthora vastatrix), but which after forty 
years has now completely lost this resisting power. Again, we 
have ample direct evidence for regarding the apparently “‘rest- 
ing”? nucleus in a cell as having the same sort of relation to the 
cytoplast as a nerve-centre has to an organism,’ a view sup- 
ported too by the fact that the nucleus approximates in 
chemical composition to nerve substance, being richer in 
lecithin and phosphorus generally than the cytoplasm. Now, 
in ordinary cell division, on the principle of continuity, there 
is no essential change in brood-cytoplast and brood-nucleus, 
and the result of repeated cell fission is merely a multiplica- 
tion of these. But we know that a nerve-centre ceases to 
respond readily to a continued or repeated stimulus of the 
same kind. It would seem then probable that, after a pro- 
longed association in life continued through a series of fis- 
sions, the nucleus would respond less readily to the stimuli 
received from the cytoplast ; consequently its directive powers 
would be diminished ; and conversely the protoplasm would do 
its work more imperfectly ; the nucleus again would be less 
nourished ; and a vicious circle of deterioration would set up 
in the cell, ending in senescence and death. Maupas has told 
us that in the senescent Ciliata the cell-body is dwarfed and 
deformed, the nuclear apparatus reduced and degenerated.* 
1 Cf. Haberland’s researches on the behaviour of the nucleus in the activity 
of the vegetable cell; Griiber’s on artificial division of Ciliata; Eimer has 
even adduced evidence to show that in nerve-centres themselves the nuclei of 
the ganglion-cells play the part of primary centres (“The Cell-nucleus as 
Central Nervous Organ,” in ‘Organic Evolution’ [Eng. Trans.], p. 349). 
2 The recent researches of Fol (‘Comptes Rendus,’ April 20, 1891), 
Guignard (‘Comptes Rendus,’ March 9 and May 11, 1891), and Flemming 
(‘ Arch. f. mikr. Anat.,’ t. xxvii, pt. 2) complete the evidence that the “centro- 
some ” of Boveri plays an essential part in mitosis and karyogamy; and the 
phrase “nucleus and centrosome” should in this section be used to replace 
“nucleus”? wherever it is used in antithesis to cytoplast in the present dis- 
cussion. 
VOL. XXXIII, PART I —-NEW SER. E 
