184 HUBERT DANA GOODALE 



disappearances of furrows, In D cleavage started in the usual way by 

 the formation of a pit on CD which gradually deepened, one part extend- 

 ing into C as already described, and the other in D. At 7 :53 another 

 depression ap])eared on the same vertical b(>low the first. Later it 

 disappeared. At 8:05, the first furrow in. this (}uadrant reached over, 

 about 45°. At 8:13, it changed its direction and became vertical at 

 its distal end. This change of direction gradually influenced the whole 

 furrow so that it became nearly vertical. Fig. lid. Turning now to 

 A, we see another remarkable series of changes. At 7:52, a (lei)ression 

 which appeared on 1 AB gave rise to a furrow extending in both direc- 

 tions. At 8:07, the furrow extended rather more than 45° towards 2 

 AD. At 8:23, a small vertical groove appeared as indicated in fig. 11a. 

 At 8:27, the original furrow had disappeared and only the depression 

 remained (fig. 11 6). This condition continued until 8:45, when the 

 groove disappeared and in its place appeared the furrow shown in fig. 1 1 

 c. Later, this changed to a furrow extending towards the lower pole 



(fig. n d). 



Egg 47, fig. 12. In quadrant C at 10:45, a horizontal furrow started 

 from 2 CD clockwise towards 1 CB, which it reached in twenty-nine 

 minutes. At the same time, a little nearer the upper pole another fur- 

 row started from the same vertical into both C and D. It extended more 

 rapidly than the first and in five minutes had gone about 25°. The first 

 went only 13 or 14° in ten minutes. However, the second furrow pro- 

 ceeded no further in C, but faded out. In D it changed its direction 

 so as to become oblique and at 11:25 had nearly reached the equator. 

 In A at 10:50, a furrow appeared on 2 AB and perpendicular to it, 

 indicating the formation of a horizontal furrow. At 10:56 there was a 

 shifting of the blastomeres in such a way that 2 AB became bent at its 

 middle, i.e., of the part above the equator. This point moved some 

 distance from its original position (cf . the furrow represented by crosses) . 

 The further progress of this furrow was vertical. In B, a vertical fur- 

 row was formed. Shiftings of the other cells occurred but were not 

 recorded at this time. 



It is difficult to interpret these shiftings of furrows. It points 

 towards a lack of complete control by the nucleus over cell divi- 

 sion. The latter may initiate cell division but the cytoplasm 

 would seem to control its further progress. Probably the de- 

 flections are produced in part by differences in the constitution 

 of the yolk. If, for example, there were more yolk granules in 

 one spot and therefore less protoplasm, the planes of cell division 

 might more easilj'' follow the more protoplasmic parts of the egg 

 which lay to one side of its projected path. It is evident, however, 

 that speculation in the subject is quite idle for the present. In 



