PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 367 



ever went ruitlier, and advocated the view tliat tlicrc is notliiiii;- in the 

 iiatiiic of \ italizatiou or ''reiuveiiesceuce" in coiijiiuatiou — that, liiveu 

 proiK'i- oii\ironiiieiit, protophisiu i.s immortal, and runs upon a course 

 of undiminished activity. This we have seen is not the casein the in- 

 fusoria, aiid, as recently remarked by Ilartog, there is only one class 

 of organisms wliich. according' to our i)resci!t knowledge, are com- 

 pletely agamous and immortal — namely, the Mouadiiia. It may in 

 future ap]>ear that e\'en in the monads there is a cycle for the develop- 

 ment in which conjugation plays its i)art. 



Maupas' experiments seem to establisli the i)rimitive, and therefore 

 the true, interpretation of the purpose of conjugation as Avell as of sex, 

 the latter being a ctmsecpience of the former, namely, that after a h)ng 

 ])eriod of direct subdivision of hereditary material from a single in- 

 dividual, a limit is reached beyond wliich the forces of heredity are 

 not reproduced in their original intensity unless cond)ined Avith another 

 set of similar fin'ces of different origin. This combination restores 

 the original intensity. It is objected to this that two sets of feeble 

 forces can not constitute one vigorous force, but this is met by the 

 observed fact that such union does start a new life cycle, and is there- 

 fore rejuvenescent. ^Va may regard this as the fundamental meaning 

 of conjugation, and the production of variations as entirely secondary. 



The distribution of the chronuitin. — We have now reviewed some 

 of the main i)henomena of fertilization; there still remains the relation 

 of the hereditary substance to the future develo])nnMit of the individ- 

 ual. There is, lirst, the astonishing fact that, as the chromatin goes 

 on diA'idiug, its mass or volume remains ai)i»arently undiminished; 

 that is, there is apparently as nuich chromatin in one of the many 

 million active cells of the body as in the original fertilized ovum, and 

 there is still an eingma as to the nature of this cliromatin and its 

 functions. Secondly, there is the x)i"oblem of the maternal and i)ater- 

 ual elements in each cell; do they lie side by side or are the.\' Insed '. 



1. In plants DeVries* and others believed that all or by far the 

 greater number of cells in the plant body contain the total hereditary 

 characters of the species in a latent condition. Kollikert has fully 

 discussed this question and called attention to ^Miillers early views that, 

 in spite of the physiological division of labor ])roducing the tissues, 

 the properl ies of all the tissues <*an be derived from the nuclear sub- 

 stance of a single tissue, as ju'oved by experiments upon the lower 

 animals. Weismann, on the other hand, has held that the course of 

 development is marked by a constant qualitative disrril)ution of his 

 germ-])lasm or hereditary substance, so that, so far as luu-lear content 

 is concerned, there are thiee forms of cells: (1) with nucleo-plasm; 

 (2) with nucleoplasm and gei'm-plasm; (.'}) with germ-i)lasm only. 



" Hugo de N'lies: IntiaiL-lhihirr I'ani^cnesis. Jena, 188!). 



t Die liedentung- der Zellkerne fiir die Vor.ijiingc der Vcn-ilmiig. /<it. f. Wiss. 

 Zool., 1885. And, Das KaryopLisiua uiid die Vcrerbung, oi>. cit.. 1880. 



