Febkttaey 5, 1897.] 



SCIENCE. 



235 



pole of the spindle commence to swell up into 

 vesicles in preparation for the reconstitution of 

 the nuclei. Then the centrospheres fade away 

 and the centrosomes with the central spindle 

 between them move further apart to opposite 

 sides of the new nucleus. At this stage we find 

 once more the enormous radiation directly from 

 the centrosomes which involves nearly all the 

 cytoplasm in the egg. 



When the new nuclei have reached the so- 

 called resting stage the centrospheres develop 

 again, the distal part of the rays break up into 

 the network, the centrosomes divide, and the 

 processes just described are repeated. 



With each cleavage a beautiful Zwischen- 

 korper is developed. It consists at first of a 

 circle of small dark bodies staining like the cen^ 

 trosomes, each with a brush of fibrils diverging 

 toward the newly formed nuclei. At a later 

 stage these bodies all become compressed into a 

 single mass and lose their individuality. 



The phenomena exhibited in the egg of Chse- 

 topterus lead me to the following conclusions : 



1. That there is in the egg a definite body — 

 the centrosome — which is not an artifact nor a 

 myth, and which is not identical with the cen- 

 trosphere or astrosphere, though the latter is 

 sometimes present. 



2. That in the oocyte of the first order, i. e. , 

 the unmaturated egg, the centrosome arises by 

 a modification of pre-existing cytoplasmic struc- 

 tures. 



3. That the centrosomes, whatever their 

 origin, are capable of growth and multiplica- 

 tion and persist through at least several cell 

 generations. 



4. That there is no union of male and female 

 centrosomes during fecundation — no quadrille 

 of the centers. The female centrosomes, on 

 the contrary, entirely degenerate, and there- 

 fore the centrosomes cannot be considered a 

 special means for conveyance of hereditary 

 qualities. 



5. The centrosomes of the first and succeeding 

 cleavage spindles are identical with, or derived 

 directly from, the male centrosomes, which are 

 probably brought into the egg with the middle- 

 piece of the spermatozoon. 



6. The centrosphere, a differentiated region 

 about the centrosome, gives a different reaction 



from the centrosomes, on the one hand, and the 

 rest of the cytoplasm on the other, both in 

 point of color and resistance to certain re- 

 agents. 



Corrosive, acetic and other reagents will 

 sometimes completely destroy the centrosphere, 

 though the rays and other structures are fairly 

 well preserved. 



The centrospheres, unlike the centrosomes, 

 come and go with each succeeding caryokinesis. 

 When they are present, the cytoplasmic rays of 

 the aster are less strongly developed then when 

 they have disappeared, and the rays diverge 

 directly from the centrosomes themselves. 



The centrosomes divide and move apart 

 . within the centrosphere for a considerable dis- 

 tance without altering the shape of the latter. 

 A. D. Mead. 



V. THE CENTROSOME PROBLEM AND AN EXPERI- 

 MENTAL TEST. 



It is now generally supposed that the centro- 

 some represents ' the especial organ of cell 

 division,' 'the dynamic center of the cell.' 

 The outcome of investigation as generally un- 

 derstood is well stated by Dr. Wilson in his 

 recent work on ' The Cell' (p. 171) : 



"From the father comes the centrosome to 

 organize the machinery of mitotic division by 

 which the egg splits up into the elements of 

 the tissues, and by which each of these ele- 

 ments receives its quota of the common her- 

 itage of chromatin. Huxley hit the mark two 

 score years ago, when, in the words that head 

 this chapter, he compared an organism to a web 

 of which the warp is derived from the female 

 and the woof from the male. What has since 

 been gained is the knowledge that this web is to 

 be sought in the chromatic substance of the 

 nuclei, and that the centrosome is the weaver at 

 the loom." 



The evidence as to the origin and function of 

 the centrosome is not all in yet, and some of 

 what is in cannot be easily reconciled with 

 these generalizations. How very diflicult it 

 is to reach certainty in observations on this 

 structure, no one knows by his own experience 

 better than Dr. Wilson himself. That the cen- 

 trosome comes from the mother in parthenos 

 genetic eggs is one fact about which no doubt 



