212 HUBERT DANA GOODALE 



distance from centre to circumference of the drawing. Hence, 

 with any movement of egg material the same amount of movement 

 of the blastopore or marks will appear much greater, the greater 

 its distance from the circumference of the drawing. If the blasto- 

 pore appears only 30° from the equator of the egg, a real move- 

 ment of 30° will appear much less than if it had appeared 50° 

 below the equator and moved an equal distance. 



The relations between the planes of cleavage and the planes of the 



embryo 



The eggs used in these experiments were marked, usually in two 

 places, on the upper hemisphere. A free-hand drawing was made 

 (except series K) upon a circle as a basis, to record the relation 

 between the marks and the plane of cleavage. Further records, 

 usually in the form of drawings, were made at intervals showing 

 the changes in shape and size of marks. When the eggs were 

 marked sufficiently far above the equator and the marks were 

 sufficiently small, they often remained nearly constant after the 

 initial spreading had occurred. But such marks were very likely 

 to fade, since they lay in the more protoplasmic parts of the eggs. 

 Marks made near the equator were not very apt to fade but the}' 

 became involved in the series of changes about the equator 

 described in another place. Hence, even with drawings, it was 

 not always possible to find a single interpretation only, of their 

 movements, from which to derive their original position. If, 

 however, the marks happened to come in certain positions rela- 

 tive to the blastopore or fell in the median plane of the embryo, 

 no misinterpretation of the data was possible. For example, 

 if the marks happened to lie in the future median plane of the 

 embryo, the mark on the blastopore side moved only a short 

 distance directly into the blastopore, while the one on the other 

 side of the egg moved in the same plane across the ventral side 

 of the egg. As the majority of eggs were marked parallel to the 

 first plane of cleavage and as all doubtful cases were discarded, 

 it may help explain why cases of coincidence between the first 



