356 



CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



The latter must, therefore, be the centres of division ; ^ though it 

 must not be forgotten that, in some cases at any rate, normal division 

 requires the presence of nuclear matter (p. io8). 



The centrosome must, however, be something more than a mere 

 division-centre ; for, on the one hand, in leucocytes and pigment-cells 

 the astral system formed about it is devoted, as there is good reason 

 to believe, not to cell-division, but to movements of the cell-body as a 

 whole; and, on the other hand, as we have seen (pp. 165, 172), it is 

 concerned in the formation of the fiagella of the spermatozoa and 

 spermatozoids, and probably also in that of cilia in epithelial cells. 

 Strasburger ('97) was thus led to the conclusion that the centrosome 

 is essentially a mass of kinoplasm, i.e. the active motor plasm,^ and 

 a nearly similar view has been adopted by several recent zoologists. 



A £ C 



Fig. 166. — Cleavage of dispermic egg of Toxopnettstes. 



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. 



Henneguy concludes that the centrosomes are " motor centres of 

 the kinoplasm " both for external and for internal manifestations.^ 

 Lenhossek regards them as " motors " for the control of ciliary action 

 as well as for that of the spermatozoon,* and perhaps also for that of 

 muscle-fibrillae.^ Zimmerman concludes that " the microcentrum is 

 the motor centre of the cell, that is, the ' kinocentrum ' opposed to 

 the nucleus as the ' chemocentrum.' " ^ Regarding their control of 

 ciliary action, he makes the same suggestion as that of Henneguy and 

 Lenhossek cited above. He adds the further very interesting sug- 

 gestions that the centrosomes may be concerned with the pseudopodial 

 movements in the epithelial cells of the intestine, and that they may 



1 This phenomenon was first observed by Ilertwig, and afterward by Driesch. I have 

 repeatedly observed the internal changes in the living eggs of Toxopneustes. 



2 Cf. p. 221. * '98, p. 107. 6 'gg^ p. 697. 



3 '98, p. 495. 



5 » 



99. P- 342. 



