KOFOID: DEVELOPMENT OF LIMAX. 61 
In spite of the examination of a large number of eggs, and the repeated 
killing of those whose age and approximate stage were known, I have not 
been able as yet to obtain an egg showing the spindles resulting in this 
division. Figures 38, 40, and 42 (Plate VI.) all represent stages sub- 
sequent to the formation of M, and the other members of the quartet 
7.9. There is some evidence, however, as to the character of the divis- 
ion. Figure 38 is a view of the vegetative pole of an egg of forty cells. 
The four central cells have seven peripheral neighbors. Deeper focusing 
reveals the presence of a large nucleus, lying within a definite cell 
boundary. This is quite below the level of the nuclei of the vegetative 
quartet. Its nucleus lies below and slightly nearer the median plane 
than that of d". The superficial extent of this deeper lying cell is 
limited to a narrow strip adjoining the cell with which it has arisen, 
i. e. it is peripheral to d^', The other members of the quartet 7.2 are 
present, and when the test for the spiral is applied it is evident that 
this is a left spiral, though the amount of the shifting is evidently not very 
great. It is quite plain that in this case the cell d7?, which gives rise to 
the mesoderm, comes from d! at the time of its division into d™ and 
d'?, As in previous stages, the quartets d and b are in contact at the 
ventral cross furrow, 
Figure 40 (Plate VI.) represents a forty-two-cell stage which has 
recently been the scene of a number of divisions. Here, as in the egg 
just discussed, the cell d"? is very large, and is crowded in toward the 
centre of the egg, lying below d”! and slightly nearer the median plane. 
It maintains a small crescentic connection with the exterior, between 
d™ and d*3, The other members of the quartet 7.2 are present, and 
show about the same nuclear conditions that d"? (= M) does. They 
are therefore of about the same age. The divisions of the cells of tho 
quartet 6.1 in this egg have evidently been very nearly equatorial, and 
unless there should be at a subsequent period some shifting of the 
mesoderm to a position nearer to the median plane, — as adopted in this 
paper, — it would be necessary to orient this egg as Rabl and Blochmann 
have oriented Planorbis and Neritina. Judging from the nuclear condi- 
tions the division has taken place quite recently. Eggs of later stages 
show that the mesoderm is generally placed bilaterally with reference 
to the eross furrows and the prevailing quadrangular form of the egg 
of those stages. The division of this quartet is in all cases unequal, the 
smaller cells lying at the vegetative pole. 
The conditions of the egg shown in Figure 42 (Plate VI.) were for u 
long time very puzzling to me. It contains forty-five cells, which 
