SOME OBSERVATIONS ON MATURATION AND 

 FECUNDATION IN CH^TOPTERUS PERGA- 

 MENTACEUS, CUVIER. 



A. D. MEAD. 



My investigations on this annelid were begun last summer 

 at the Marine Biological Laboratory, at Woods Holl, Massa- 

 chusetts. I wish here to express my appreciation of the kind 

 assistance given me by my friend Dr. W. M. Wheeler, and to 

 thank Mr. George Gray, who procured for Dr. Wheeler and 

 myself an ample amount of beautiful material. My own 

 material having been collected for the cleavage stages, Dr. 

 Wheeler generously turned over to me all that he had pre- 

 served for the study of maturation and fecundation. 



The eggs were fixed with picro-acetic acid, and stained with 

 Heidenhain's iron-alum haematoxylin and " Orange G." 



Until the entrance of the spermatozoon the egg remains 

 with the first maturation spindle in the equatorial-plate stage. 

 There are nine chromosomes arranged in a circle, with eight at 

 the periphery, and one in the center. Later, there are at each 

 pole of the spindle, nine chromosomes, which have the same 

 arrangement. Converging protoplasmic rays, meeting at a 

 dark spot at either end of the spindle, are at first perfectly 

 clear. During the later stages of karyokinesis, two centro- 

 somes, connected by a whitish band, are clearly distinguishable 

 at the inner end of the spindle. They gradually separate from 

 each other. A dark spot (centrosome ?) lies in the polar 

 globule at the outer end of the spindle (Fig. i). Meanwhile, 

 the young male pronucleus, provided with a centrosome and 

 radiations, approaches the animal pole, its centrosome some- 

 times preceding, but often following the pronucleus (Fig. i). 



Before the second polar globule is expelled the male centro- 

 some divides, and very conspicuous fibres are seen to radiate 

 from the surrounding dark-colored archoplasm. A single 



