294 



niK AMKEICAX NATURALIST [Vol. LI 



addition of fiirtlicr evidence which warrants a changed 

 interpretation of certain facts. 



Loeb first calls attention to the exclusively maternal 

 character of the early development of enucleated frag- 

 intiits of eggs when fertilized by sperm of a different 

 species. Such evidence has already been treated above 

 (p. 5). 



His second claim— that the rate of cell division and de- 

 velopment is determined only by the egg c>i;oplasm— 

 warrants fui-ther consi<lerati()n. An egg from a line in 

 whicli segiiuiitation of tlie egu' takes phice eiglit liours 

 after fertilization wa- t'ei-tilized hy siierm from a line in 

 which segmentation l)egins in ."10 minutes. The rate of 

 these cross-fertilized eggs was 8 hours, like tlie mother's 

 line. 



The careful and long continued work of Newman ( '14) 

 has, on the other hand, shown that the entrance of sperm 

 of a different species does materially alter the rate of de- 

 velopment. 



Tn l)otli refi]^i-ooal ornsses between Fundulus heteroclitus anrl F. 

 7yiajalis the rate of (lc\('l(>])ineiit of the hybrids was internie.liate between 



In the cross F. licfcroditHS X F. dniplKunis '^botli recip- 

 rocal crosses have a higher rate tlian the pni'e l)re(l strain. 

 Similarly, when we make reciprocal ci(i>>t's between Cy- 

 pronodon and any species of Fund ul us we iind a marked 

 retardation in developmental rate in both crosses. ..." 

 It is of the greatest significance that in all three cases the 

 results of reciprocal crosses were equal. Either both 

 were intermediate, botli were accelcM'ated oi- l)oth wei-e 

 r. tanl.Ml re-ardh-^ of whi<-h >|.ecie^ wa< a> th.' egg- 



parent. In tlie fac of >uch evi.lelK-e. a theory of excln^ive 

 cotuful of the eu- over earlv ,h'veh.pnient i> nntenabh". 



Xewti.an'^ fnn.lnhi.^ hvlirid,^. whih- .h'tnon^t rating the 

 cniwhr^ion jnM >tat.M]. ,Io not foi-tn critical ovi<lence for 

 (lett/rniining tlu' action in lici-edity of -iich ratc^-chai'acters 



