378 T. H. MORGAN AND UM6 TSUDA. 



I. Whether the pigment bore any fixed relation to the first 

 furrow, and by this to follow out approximately the first furrow 

 in the later stages. 



II. The relation of the dorsal lip of the blastopore to the 

 pigment and to the first furrow. 



I have examined a large number of eggs in the early stages, 

 in order to ascertain the exact appearance of the pigment, and 

 to compare it with the later stages. When the egg is looked 

 at on the under and non-pigmented side, with the lower pole 

 turned uppermost, the line of pigment, extending, as it does, 

 nearer to the lower pole on one side than on the other, has a 

 crescentic outline. The pigment zone or band is not usually 

 visible on the opposite side (see fig. vi). The same crescent- 

 shaped appearance of the pigment is easily followed in the later 

 stages up to the formation of the blastopore, at which time there 

 is a rapid growth of pigment downward towards the lower pole. 

 In order to ascertain what relation the first furrow bears to 

 this crescent-shaped band of pigment, I examined 119 pre- 

 served eggs, as well as a number of living ones, in the stage 

 when the second furrow had begun to come in from the upper 

 pole and was about to meet the first furrow on the lower side. 

 I made my observation on the eggs just before the two sides of 

 the second furrow had met and intersected the first furrow at 

 the lower pole, but when they were near enough to meeting, so 

 that the point of the lower pole could be approximately judged. 

 In this vvay I was able to distinguish the first furrow from the 

 second, which would not have been possible after the second 

 cleavage was completed, and at the same time I could guess 

 approximately the position of the lower pole, the meeting- 

 point of the first and second furrows. 



The first furrow does not seem to cut the pigment zone bi- 

 laterally ; nor does it, on the other hand, always divide the egg 

 into a lighter and a darker half. Out of the 119 eggs 

 examined, in 76 cases the first furrow cut through a little 

 to one side of the central point of the crescent, only 

 approximately dividing the pigment. 



Figs. A, B, and c sliow diagrammatic views of the lower 



