THE FERTILIZATION PROCESS IN THE SNAIL. 89 



the metaphase of the second maturation and the former after the 

 second polocyte had been extruded. Fig. 58 shows a first polocyte 

 of undetermined age in which six chromosomes appear as pairs 

 and others have probably been divided so long that the halves are 

 now completely separated, thus bringing the apparent number up 

 to about eighteen. Whether or not this high number of chromo- 

 somes is due to monaster activity is not known. However, a first 

 polocyte which has undergone monocentric division is shown in 

 Fig. 59, and another is shown in monocentric metaphase in Fig. 

 34. The chromosome vesicles in the second polar body have 

 disappeared and fusion of the egg karyomeres is nearly complete 

 in Fig. 35, while in Fig. 34 these conditions are not so far ad- 

 vanced. 



The foregoing observations indicate that there is an actual time 

 relationship between the age of the first polocyte and the apparent 

 number of chromosomes it contains and that this relation holds 

 true until the pronuclei are formed. No further data on this 

 point are available than the first cleavage nucleus (Fig. 42). 

 However, the chromosomes in the first polocyte apparently dis- 

 integrate soon after having undergone monocentric mitosis and 

 before the first cleavage. 



b. Second Polocyte. -In Fig. 60 ten chromosomes are shown 

 remaining in the egg during the second maturation anaphase. I 

 am at a loss to explain the apparent number and pseudo-equatorial 

 plate formation of the chromosomes which are being extruded 

 in this instance. The pseudo-equatorial plate really lies more 

 nearly on its edge than is shown in Fig. 60. Successive changes 

 in the second maturation anaphases are shown in Figs. 61-63. In 

 each case approximately ten chromosomes are destined to be ex- 

 truded and as many to be left in the egg. The chromosomes 

 left within the egg, as well as those within the second polar body, 

 form vesicles containing chromomeres (Figs. 26-37, 4)- The 

 vesicles of the second polar body appear to lose their membranes 

 and thus set the chromomers free within the cytoplasm of the 

 polocyte (Figs. 35, 42). 



c. Karyomeres. The chromosome vesicles or " karyomeres " 

 (Conklin, '02) of the egg nucleus, which form after the extrusion 

 of the second polar body, offer some evidence for determining the 



