PRESENT I'KOliLHMS IN EVOLUTION AND HEREDITY. ')G1 



growth and (li\i(U's by (Mmstrictioii. and tlic (iii) tiiicroiiKchus (paranu- 

 cleus, nucleolus, of authors), uliicli i)r('sides over the preservation of 

 the species. The hitter contains chromatin; it is the seat of vejuve- 

 nescence, the hasis of liere<lit\', it divides by mitosis, sliow inu' all the 

 typical stages of kav> okinesis <'xcepting the loss of the cell mendjrane. 



The trausformation iu each of these copulating cells first alfects the 

 centers of hereditary substance, viz, the micro-nuclei ; they divide three 

 times; thus the micronuclear substance is reduced to one-fourth of its 

 original bulk. It is contained in two surviving micronuclei (the others 

 being absorbed or eliminated), one of which migrates into the adjoin- 

 ing cell: the other remains stationary. This migration is followed by a 

 fusion of the migrant and stationary micronuclei; this fusion efi'ects a 

 complete interchange of hereditary substance, after which the tw^o in- 

 fusoria separate and enter upon a new life cycle. Meanwhile the me- 

 ganucleus breaks up and is reconstituted in each fertilized cell. 



Maupas gathers from these interesting phenomena additional ])roof 

 that the chromatin of all cells bears the inherited characteristics and 

 that the cyto-j)lasm and nucleoplasm, or achromatin, is the dynamic 

 agent, because the micronuclei bearing the chromatin are the only strnct- 

 iires which are permanent and persistent, all the other structures — 

 nucleo-plasm, archo-plasm, etc. — being replaced and i-enewed. The re- 

 duction of the chromatin is purely (piantitative, the eliminated ami fer- 

 tilizing micronuclei being exactly equivalent; after the chromatin has 

 been quartered the cell becomes incapable of further activity until it is 

 reinlcrced by chromatin from the copulating (;ell. 



No distinction between the sexes in heredity. — The three laws 

 which underlie these iihenomena are: (1) That fertilization consists in 

 the union of the hereditary substance of two individuals. (!') That 

 before the union the hereditary substance in each is greatly reduced. 

 (3) Tliat there is no line between male and female, the conjugating cells 

 are simply in a similar physiological condition wherein a mingling of 

 hereditary characteristics alfords a new lease of life. As iVIaupas says : 



"Les differences appelees sexuelles portent sur des faits et des 

 phenoinenes ])urement accessoires de la fecondation. La fecondation 

 consiste iiniquemcnt <lans la, r(''uuion et la (copulation de deux noyaux 

 semblables et equi\ alents, mais provenus de deux cellules distinctes." 



In this coiu-lusion as to the secondary and sui)erficial, rathei' than 

 fundamental, difference between the two sexes, Maupas sim[)ly con- 

 firms the views of Strassbiirger, the botanist, Hensen, R. and O. llert- 

 wig, Weismann, and others, namely, that sex has (^.volved Irom the 

 necessity of cell conjugation; that even in the higher forms the cells 

 born by the two sexes are absolutely neutral so far as sex is concerned, 

 the wide difference of form of the germ cells is a result of i)hysiological 

 division of labor — the mass and yolk of the ovum having been dilfer- 

 entiated to supi)ort the early stages of development while the sperma- 

 tozoon has dispensed with all these accessories and acquired an active 



