502 THOMAS H. BRYOK. 



to the &gg, or by disturbing the general equilibrium in some 

 such way as the loss of water does, when the normal osmotic 

 relations arc disturbed ? Or does the spermatozoon carry into 

 the egg some specific chemical substance which produces a 

 local differentiation, of which the centrosome and the aster 

 are the expression? Or docs it import " a highly active centro- 

 some or centroplasni about which the cytoplasmic energy is 

 brought to a focus ? " 



Boveri (1902) holds that a genei'al stimulation of the ogg, 

 with the sperm head as the poiut of predilection for the 

 formation of the aster, as in mngnesium eggs the egg uucleus 

 is the point of predilection, is insufficient as an explanation. 

 There is much rather something special present in the sperma- 

 tozoon, which determines that the aster shall appear at that 

 point, and that point only ; and thus he thinks that still the 

 appearances may best be described as beiug due to the intro- 

 duction of a centrosome. Even admitting — which, as has just 

 been indicated, he does not — that the spermatozoon acts like 

 Loeb's agents, and in view of the demonstration by Morgan 

 and Wilson that their effect is to cause the egg to produce 

 centrosomes de novo, only a modification of secondary 

 importance would be required in his theory of fertilisation, 

 viz., that instead of saying that the spermatozoon brings a 

 centrosome into the egg, it would be necessary to say that it 

 causes the formation of a centrosome in the egg, from the 

 division of which the rest follows. 



Taking the sperm aster as the manifestation of activities 

 produced by the spermatozoon, and looking to its sharp 

 localisation on the site of the middle piece, it seems reason- 

 able to suppose that the localised excitement is the effect of .an 

 agent operative in fertilisation, and that it is probably related 

 to the middle piece ; but the actual continuity between the 

 centrosome of the spermatozoon and that in the aster ha.s not 

 l)een absolutely demonstrated, and the now facts in regard to 

 the centrosome put the matter in another light. Thus it 

 remains for the future to decide which of the two latter 

 alternatives stated above shall be adopted, and perhaps after 



