r 

 f 



LINVILLE: PULMONATE GASTEROPODS. 225 



mention of the differences in the character of the division of the chro- 

 mosomes in the first as compared with the second maturation spindle. 



Turning now to the question of the centrosonie, I iind that after the 

 first polar cell has been nearly or quite formed the centrosphere belong- 

 ing to it, when it can be made out at all, gives evidence of disintegra- 

 tion. This is shown in Plate 2, Figure 8. Nothing which can be 

 maintained to be a centrosome appears in the outer centrosphere of the 

 polar cell. There is, however, in Plate 2, Figure 12, in the only polar 

 cell represented in that figure, a distinct centrosome, with fibres radiat- 

 ing to the chromosomes. The region of the supposed connection of the 

 polar cell with the egg in this section was covered by a mass of foreign 

 substance, so that it is not certain, though highly probable, that the 

 polar cell was joined to the egg. The aster remaining in the egg shown 

 in Figure 8 resembles the condition of the centrosphere shown in Figure 

 21. In the present case (Figure 8) the centrosphere may be said to be 

 composed of two parts, a very small, central clear area, of spherical 

 form, and a very much larger non-spherical enveloping structure. The 

 two are not concentric, the inner sphere being much nearer to the 

 peripheral flattened wall of the enveloping structure than to its deep 

 rounded extremity. It is to be observed that in Figure 8, at the exact 

 centre of the inner, small centrosphere, there is a minute centrosome, 

 but with no indication of division in preparation for the next matura- 

 tion spindle. The inner centrosphere, though small, is very distinct. 

 Within this centrosphere no rays could be distinguished ; in fact, the 

 contents, under the highest magnification, appeared to be entirely 

 homogeneous. Eather prominent rays, few in number, can be seen 

 passing from the periphery of the inner centrosphere out through the 

 outer or enveloping structure. This outer structure stretches from the 

 plane of the deep ends of the series of chromosomes belonging to the eggf 

 toward the centre of the egg, a distance equal to nearly twice its width. 

 The walls, beginning at the chromosomes, run for a short distance per- 

 pendicular to the plane of the chromosomes and then gradually converge 

 and nearly come together, but the lines bounding this outer centro- 

 sphere decrease in distinctness in passing from the plane of the 

 chromosomes. The outer structure is to be conceived of as a cylinder, 

 truncate at the peripheral end, dome-shaped at the deep end, and con- 

 taining a spherical inner centrosphere located much nearer the truncate 

 than the opposite end. 



The enlargement of the centrosphere during the completion of the 

 polar cell and after its formation — an occurrence so striking in Limax 



