258 SOME ASPECTS OF CELL-CIIEMISTKY AND CELL-PHYSIOLOGY 



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



either or both parents. , • i .4. 



Boveri ('89. '95, i ) has attempted to test this cone usion by a most 



ingenious and beautiful experiment; and although his cone usions do 



^ not rest on absolutely certam 



ground, they at least open the 

 way to a decisive test. The 

 Hertwig brothers showed that 

 the eggs of sea-urchins might 

 be enucleated by shaking, and 

 that spermatozoa would enter 

 the enucleated fragments and 

 cause them to segment. Boveri 

 proved that such fragments 

 would even give rise to dwarf 

 larva;, indistinguishable from 

 the normal in general appear- 

 ance and differing from the 

 latter only in size and in the 

 very significant fact that their 

 nuclei contain only half the nor- 

 mal number of chromosomes. 

 Now, by fertilizing enucleated 

 egg-fragments of one species 

 {SphcvrccJiinus granulans) with 

 the spermatozoa of another 

 ( Ecliiniis Diicrotiiberculatns), Bo- 

 veri obtained in a few instances 

 dwarf Plutei showing purely 

 paternal characteristics ( h ig. 

 116). From this he concluded 

 that the maternal cytoplasm has 

 no determining effect on the 

 offspring, but supplies only the 

 material in which the sperm- 

 nucleus operates. Inheritance 

 is, therefore, effected by the 

 nucleus alone.i Boveri's result 

 is unfortunately not quite conclusive, _ as has ^een pointed^^^t 

 bv Seeli-er and Morgan, yet his extensive experiments establish, 1 

 hink a s? ong presumption in its favour. Should they be positively 

 fonfii-med, the' would furnish a practical demonstration of mheritance 

 through the nucleus. 



Fig. 116. — Normal and dwarf larvte of the 

 sea-urchin. [BOVERI.] 



A. Dwarf Pluteus arising from an enucleated 

 eg<^-fragment ot Sp/uerechnnis gra>ii<Iaris. fertilized 

 widi spermatozoon of Echinus microiuberculatus, 

 and showing purely fatcmal characters. B. N' or- 

 mal Pluteus oi Echinus mu-rotuhcrculatus 



1 The centrosome is left out of accou.t, since it is frcquentlv derived from one sex 



oui 



