KOFOID: DEVELOPMENT OF LIMAX. 67 
As stated in my earlier paper (94, p. 191), there are some indica- 
tions in Rabl's work that Planorbis presents a case of reversed cleavage, 
i. e. the cleavage is such that the spirals of the even generations are left, 
and those of the odd right. Fol’s ('S0) figures of the eight- and six- 
teen-cell stages of this Pulmonate (Plate IX.-X. Figs. 1, 2) indicate 
that the spiral of the fourth generation is a left one, and that of the 
fifth a right one. My own sketches of Planorbis, made from living 
CLEAVAGE OF CAVOLINA. 
Fol (75). 
Fou’s NOMENCLATURE, REVISED NOMENCLATURE. 
Gener- [Number 
ation, of 
Spirals. Cells. Yun Cells, Spirals. 
Ir uu 1 6.4 j 
Left. gro D. | VE 1 EA att m Right. 
5.4 
Right. y >] 16. |. < qna Left. 
r V. ji 
d a 
Left. rol 12 | T «5, Left. 
Right phe My Right 
8116, 7 . VO hight. 
E Left. 
Z, II, HT, IV. II. 4 | A, D, O, D. | Division oblique, 
cells in one plane. 
eggs in the spring of 1892, show the same direction in these spirals, 
So far as can be judged from these facts, the alternation of spirals 
holds in this case, which is probably one of reversed cleavage. 
If the reversed spirals persist until the formation of the mesoderm, this 
germ layer would then come from the right posterior macromere, instead 
! Fol does not name or discuss spirals. The nomenclature in this column is 
deduced entirely from his lettering of the cells. After the third generation the 
divisions of only one quadrant (7) are followed. In this, as in the following tables, 
sapital letters indicate macromeres, and the lineage of only a single quadrant (a of 
the revised nomenclature) is given. 
