KOFOID: DEVELOPMENT OF LIMAX. 83 



gi-adually accomplished, occupying in one instance recorded about five 

 minutes, no trace of the extruded liquid is visible. I have observed in 

 the two-cell stage the expulsion of the liquid at both animal and vegeta- 

 tive poles, but never at both poles of an egg at the same time. Warneck 

 ('50) and Fol ('80) both state that the contents of the cavity are ex- 

 pelled at the vegetative pole. This is cei-tainly by no means constant, 

 and I am inclined to believe that in a majority of cases, especially in the 

 later stages, the elimination takes place at the animal pole of the egg. 



This ephemeral cleavage cavity is not confined in Limax to the two- 

 cell stage, but is equally prominent in the stages immediately following. 

 The passage of the egg from the two- to the four-cell stage may be 

 accompanied by au incomplete elimination of the contents, for I have 

 often observed cases where a small cavity persists throughout the 

 progress of this cleavage. 



P'igures 8-13 (Plate I.) show the history of the cleavage cavity in a 

 diff'erent egg from the one observed during the two- to four-cell stage. 

 At 3.15 p. M. there was no trace of any cleavage cavity, and the second 

 cleavage furrow had almost reached the vegetative pole. Half an hour 

 later the characteristic four-cell condition had been reached (Fig. 8), 

 and in ten minutes more a cleavage cavity of considerable volume was 

 developed in the vertical axis of the egg. This continued to increase in 

 size until 4.45 p. m. (Figs. 9-11), when a total expulsion of the contents 

 occurred, occupying not more than thirty seconds (Fig. 12). The nuclei 

 at this period were at the amphiaster stage. Within fifteen minutes a 

 new cavity had appeared in the now elongated vertical axis of the egg. 

 This cavity was at first very narrow and extended almost from pole to 

 pole. It increased slowly in volume, but was not wholly obliterated at 

 the division into eight cells, which occurred at 5.38-5.45 p. m. (Fig. 13). 

 It is not at all unusual to see the total elimination of the contents of 

 the cavity at the division into eight cells, but the occurrence is not 

 constant. The configuration of the cavity of the four-cell stage as 

 viewed from the animal pole is shown in Plate II. Fig. 17. It is almost 

 rhomboidal in outline ; the angles lie at the cleavage planes, and the 

 sides are curved with the convexity next the cavity. It is probable that 

 a partial expulsion, or perhaps a total one, has already occurred, for 

 the cavity was not very large and the nuclei were in the early phase 

 of metakinesis when the egg was killed. When the cavity is at its 

 maximum it assumes very nearly a spherical shape, i. e. the bounding 

 cells are concave toward the cavity, and they present more nearly the 

 character of a wall of uniform thickness (Fig. E, p. 81). No case has 



