Rickett.—Fertilization in Sphaerocarpos . 247 
except for their smaller size, resemble the egg nucleus in the first or second 
phase. The chromatin is arranged in the form of small granules and delicate 
twisted threads, without any definite reticular structure (Fig. 20). 
As the daughter groups of chromosomes separate, and the daughter 
nuclei are formed, the central dense mass of the cytoplasm seems to pull out 
between them, leaving only some coarse strands extending from one 
daughter nucleus to the other. In some cases these strands are fine enough 
to resemble the central fibres of an ordinary spindle, though they are never 
very numerous. Each daughter nucleus is still surrounded by a mass of 
homogeneous cytoplasm, which radiates in all directions so as to form a sort 
of star-shaped figure. It is interesting to note that the figures of Campbell 
( 1888 ) for Pihdaria gtolmtifera and of Meyer ( 1911 ) for Corsinia marchanti- 
oides illustrating two-celled embryos show a condition of the cytoplasm in 
the daughter cells very similar to that just described for Sphaerocarpos . 
The condition is illustrated in Fig. 20. 
In seven cases, all belonging to Series D, the dense substance was 
replaced by masses of granules as previously described. These are not 
arranged regularly in rows, and seem larger and closer together than those, 
for instance, shown in Fig. 11 ; but they maintain in the cell the star¬ 
shaped arrangement just described. Often they are very closely massed 
upon the new wall separating the daughter cells. 
No cases were observed in which the cell plate or dividing wall 
extended only partly across the cell. I11 all cases in which a division 
membrane was present at all, it cut the cell completely into two, and was' 
fairly distinct and heavy. 
The two-celled embryo measures about 75 by 25 y, and is therefore 
considerably larger than the egg in the first phase of fertilization. The 
enlargement is gradual, the egg in each successive phase being a little larger 
than in the preceding one (compare Figs. 2, 8, 18, and 20. Many sections, 
of course, do not pass through the greatest length of the egg). 
Eighth Phase. 
In each of the four cases found showing a division in the two-celled 
embryo, one of the nuclei had begun to divide before the other. In three 
of these cases the upper nucleus was dividing, in the fourth the lower. 
Very distinct fibres were visible in three of these cases, arising in the cyto¬ 
plasm of the dividing cell and spreading out from two fairly definite poles 
over the nuclear membrane. The chromatin was observed both in the form 
of a spireme, still enclosed by the nuclear membrane, and in the form of 
chromosomes arranged in an equatorial plate upon a typical spindle. The 
latter stage is illustrated in Figs. 21 and 22. Fig. 21 shows a polar view of 
the equatorial plate. The chromosomes are more slender than in the first 
embryonic division. Fifteen chromosomes can be counted ; of these, either 
