ÏLe maturation and fertilization of the egg of Cerebratulus. 453 



for the very reason that they were without indications of asters, and 

 therefore not to be distinguished from other granules of the neigh- 

 borhood. It would then follow that the two minute asters which they 

 did find in a very few of their preparations and which they describe 

 in the paragraph quoted above, were those which were beginning to 

 develop into the cleavage-asters, and not the identical asters (though 

 the centrosomes may have been the same) which were seen to develop 

 about the sperm-nucleus. That such is actually the case in Cere- 

 hratulus there is every reason to believe; for we find here stages in 

 which the centrosomes of the sperm-asters can be found in their final 

 positions (in the angles between the fusing germ-nuclei) and in which 

 the connection between the centrosomes and the degenerating aster- 

 fibres has been entirely lost. In such cases there is a broad area, 

 without trace of radiations , between the centrosomes and the inner 

 ends of the aster-fibres (Figs. 25 — 27). In the stage following this, 

 as stated above, the centrosomes are lost (Figs. 28, 29). Finally, 

 after the germ-nuclei have fused, a pair of minute centrosomes with 

 slender radiations about them, are found almost exactly in the position 

 occupied by the spcrm-centrosomes when last seen (Figs. 30 — 32), 



An account of the maturation and fertilization of the egg of 

 Arenicola marina just published in the Trans. New York Acad. Sei. 

 (36) agrees very closely with the observations recorded above. As 

 sometimes happens in Cerebratulus, so Child finds in Arenicola 

 that one of the asters arising from the division of the sperm-aster 

 remains near the sperm-nucleus while the other moves off a con- 

 siderable distance. The two asters remain connected with each other 

 by a spindle, however. Later the centrosomes of these asters dis- 

 appear, and the polar regions of the spindle are occupied by a fine 

 cytoplasmic network. A little later there is no trace of centro- 

 somes, true asters, or spindles anywhere in the egg. 

 Just before the germ-nuclei come in contact, two extremely minute 

 asters appear in the plane of copulation one on either side of the 

 germ-nuclei. From the region of the germ-nuclei a series of radiations 

 (which have no relation with the new asters) extend in all directions 

 towards the periphery of the cell, as was noticed above for Cere- 

 hratulus. Child considers these rays as entirely independent of 

 any true asters, and as an expression of some peculiar activity 

 of the cell - protoplasm. In Cerebratulus they are certainly the 

 remains of the degenerating sperm-asters. The author is "inclined 



