SUMMARY AND CONCLUSION 



26l 



somes of the fibres must be in some manner polarized by an influence 

 emanating from the centrosome, but in the present state of know- 

 ledge it would be useless to speculate on the nature of this influence. 

 One fact, however, should be borne in mind, namely, that the centro- 

 some differs chemically from the substance of the fibres as shown by 

 its staining-reactions ; and this may form a clue to the further inves- 

 tigation of this most interesting problem. 



The principal point in connection with our present theme is that 

 the centrosome cannot be regarded as taking any important part in 



Fig. 118. Cleavage of dispermic egg of Toxopneustes. 



A. One sperm-nucleus has united with the egg-nucleus, shown at a, b ; the other lies above. 

 Both sperm-asters have divided to form amphiasters (a, b and c, d). B. The cleavage-nucleus 

 formed by union of the three germ-nuclei, is surrounded by the four asters. C. Result of the first 

 cleavage, the four blastomeres lettered to correspond with the four asters. 



the general metabolism of the cell, nor can it be an organ of inheri- 

 tance ; for on the one hand it is absent or so small as to be indistin- 

 guishable in many actively metabolizing cells, such as those of the 

 pancreas or kidney, or the older ovarian eggs, and, on the other hand, 

 in fertilization it may be derived from one sex only. The conclusion 

 regarding inheritance would not be invalidated, even if it could be 

 positively shown that in some cases both germ-cells might contribute 

 a centrosome ; for a single case of its one-sided origin would be con- 

 clusive, and many such are actually known. 



D. SUMMARY AND CONCLUSION 



All of the facts reviewed in the foregoing pages converge, I think, 

 to the conclusion drawn by Claude Bernard, that the nucleus is the 

 formative centre of the cell in a chemical sense, and through this is 

 the especial seat of the formative energy in a morphological sense. 

 That the nucleus has such a significance in synthetic metabolism is 

 proved by the fact that digestion and absorption of food, growth, and 



