428 BASHFORD DBSAN. 
variations were found, and every attempt to reduce them toa 
common type was unavailing. Numerous horizontal cleavages 
occur in all blastomeres; increments to the cell disc are not 
lacking from the floor of the segmentation cavity. In the 
section in Pl. 31, fig. 26, a cell is seen to be budding out of 
the germ-yolk region at m, and at m’ a dividing nucleus in 
the same region is clearly comparable to a merocyte. A study 
of living material demonstrates one of the steps in the transi- 
tion from the fifth cleavage, i.e. the usual mode of division of 
the marginal blastomeres. These may be seen to bud off their 
polar ends, which, in turn, join the central cell mass, and leave 
as their outer boundary a furrow similar to that outlining the 
central blastomeres in the preceding stage. It is evident from 
the section of Pl. 31, fig. 26, that the area of the segmenta- 
tion cavity, sc., has greatly enlarged, although as a cavity it 
is no longer marked as in Pl. 81, fig. 25; the blastomeres are 
now directly apposed to the germ-yolk area. 
Seventh Cleavage (Pl. 30, fig. 8).—Horizontal and verti- 
cal cleavage planes pass irregularly through the cells of the 
germinal disc. Nuclei occur (PI. 31, fig. 27) in the germ-yolk 
area(m, m,m.) and bud off blastomeres to the overlying cell disc, 
and are seen to be undergoing direct division. The segmentation 
cavity (sc.) has now a flooring of a single layer of irregular 
blastomeres derived mainly from the germinal yolk. 
Eighth Cleavage (PI. 30, fig. 9).—By this stage the blas- 
tomeres have so subdivided that in surface view they can be 
but obscurely defined; marginally, however, they extend no 
further than in the earlier cleavages. Sections of this stage 
show that the cell-cap has increased in thickness (PI. 31, 
fig. 28) ; anumber of irregular blastomeres, yolk-laden, are seen 
in process of being budded off from the floor of the segmentation 
cavity, and numerous yolk nuclei are apparent. The segmenta- 
tion cavity (sc.) extends irregularly among the blastomeres. 
Subsequent stages of segmentation correspond closely with 
that last described, the blastomeres continuing to subdivide, 
aud at the same time to encroach slowly on the yolk region of 
the egg. 
