62 THE PHYSICAL BASIS OF INHERITANCE 



equal distribution of paternal and maternal chromatin to all 

 the cells of the offspring, we find the physiological explanation 

 of the fact that every part of the latter may show the 

 characteristics of either or both parents " (Wilson, 1900, 



P- 352). 



4. Argument from Boveri's ingenious experiment. — Taking a 

 hint from the experiments of the brothers Hertwig, who showed 

 that non-nucleated fragments of unfertilised sea-urchin ova 

 (broken by shaking) might be successfully fertilised and might 

 segment, Boveri (1889, 1895) showed that such fertilised frag- 

 ments developed into dwarf, but normal, larvae. In these, as 

 T. H. Morgan (1895) afterwards showed, the nuclei contain only 

 half the normal number of chromosomes, having had only a 

 sperm-nucleus to start with. 



Interesting as this was, Boveri's further experiment was yet 

 more striking. He fertilised the enucleated egg-fragments of 

 one species of sea-urchin {Sphcer echinus granularis) with sperma- 

 tozoa of another species {Echinus microtuherculatus), and ob- 

 tained in a few cases dwarf larvae (plutei), which showed, except 

 as regards size, the paternal characters only. Ttierefore he 

 concluded that the nucleus is the exclusive bearer of the here- 

 ditary qualities, for it seemed from the experiment that the 

 enucleated maternal cytoplasm had remained without specific 

 influence. 



It is admitted by Boveri himself that further experiments are 

 necessary, and it must be granted also, as has been pointed out 

 by Seeliger, Morgan, and Driesch, that in cases of hybridism, as 

 in Boveri's experiment, there may be a marked illustration of 

 what is called unilateral or preponderant inheritance. While 

 most hybrids are intermediate, some " take after " the father 

 and others after the mother. But the experiment remains 

 uncontroverted, if unsubstantiated, and it is as suggestive as it 

 was ingenious. 



Generally accepted Conclusion. — The general conclusion 



