454 WESLEY R. COE, 



to regard the cleavage centrosomes as new formations, and as not 

 related to the 'male' centrosomes" ^ ). 



In looking over the further literature of this subject we find that 

 in the eggs of many other animals the sperm-asters disappear entirely 

 or sufier a great diminution in size and distinctness at a stage im- 

 mediately preceding the fusion of the germ-nuclei, or at some pre- 

 vious stage. 



An interesting example of the early disappearance of the sperm- 

 asters is furnished in the egg of Pleurophyllidia as described by 

 MacFakland. In this case a minute aster makes its appearance near 

 the spermatozoon soon after its entrance into the egg. This aster 

 leaves the sperm-nucleus and moves towards the center of the egg, 

 meanwhile dividing into two independent asters. These separate 

 widely without visible connecting fibres and without regard to the 

 position of the sperm-nucleus, which has remained near its point of 

 entrance. After wandering about the egg-cell for some time in a 

 seemingly aimless manner, these two asters suddenly disappear from 

 view 2). Somewhat later, after the polar bodies have been formed, 

 the aster of the second polar spindle which remains in the egg, having 

 already lost its centrosome, likewise disappears. Then follows a stage, 

 while the germ-nuclei are maturing, in which neither centrosomes nor 

 asters can be detected anywhere in the whole egg. MacFarland 

 feels confident, however, that the centrosomes which originated from 

 the spermatozoon still lie somewhere in the cytoplasm although because 

 of their lack of radiations they cannot be distinguished from other 

 granules of the cell. Soon two new asters appear, the centrosomes 

 of which are to become the poles of the cleavage spindle. These 



1) Child's conclusion that the centrosome is not a permanent organ 

 of the cell is thus quite in accord with the views of Caknoy & Lebrun 

 (4), Mead (20), Reinke (22), Watase (29, 30) and others, and with 

 Lillie's observations (37) on the egg of JJnio. 



2) "Die Sperma-Astrospharen haben mit der Wanderung des 

 Spermakerns offenbar nichts zu thun. Wie oben erwähnt, rücken die 

 beiden Centrosomen in äusserst variabler Weise von einander und vom 

 Spermakern weg. Während der Bildung des zweiten Riclitungskörpers 

 verschwinden ihre Astrosphären vollständig. Es ist nicht die leiseste 

 Spur mehr davon zu entdecken, und es war mir deshalb von diesem 

 Zeitpunkt an nicht mehr möglich , die beiden vom Spermatozoon ge- 

 lieferten Centrosomen noch nachzuweisen. Denn ich habe keine dif- 

 férentielle Färbung gefunden, durch welche Centrosomen ohne Strahlen 

 auffindbar sind." 



