226 HUBERT DANA GOODALE 



curved. It is noticeable, moreover, that the distal end retains 

 approximatel}^, its original shape and size. 



About two days later. May 14, 1 :30 p.m. (figs. 54-55), a slightly 

 imperfect embryo had appeared on the upper surface of the egg. 

 Further changes in the marks have taken place. The blasto- 

 pore has shortened and at the same time A and D have swung 

 dorsally, coalescing with F and E, respectively. B and C have 

 continued the movement blastopore-wards, but now, in part 

 at least, the advance has been one of the band as a whole. The 

 distal end has moved closer to the blastopore, which results in 

 a shortening of the bands. This shortening is correlated with 

 the elongation of the embryo, which has taken place meanwhile. 

 In fig. 55, the anterior connective lies out of sight, just beyond 

 the lower edge of the drawing. 



All the eggs marked in this way show similar movements which 

 vary only in details. The lower hemisphere of the eggs of the 

 first series described above were studied by inverting the egg 

 at intervals. To avoid this necessity', the eggs of the other 

 series, illustrated by figs. 56-63 were placed on an inclined mirror 

 in a Stender dish filled with water and the image of the lower 

 hemisphere studied with the microscope. The use of this mirror 

 has one serious objection aside from a certain indistinctness of 

 the image. The mirror reflects only part of the lower hemisphere, 

 the missing part being the equatorial region furtherest from the 

 mirror. At the opposite side of the egg, a little of the upper 

 surface is reflected. Thus, the circumference of the drawing of 

 the lower hemisphere does not represent the real equator of the 

 egg as it does in the drawing of the upper hemisphere. The eggs 

 although unable to rotate freely within their membranes, were 

 free to adjust themselves to gravity, as care was taken to prevent 

 them from becoming attached to the mirror's surface. Conse- 

 quently, it was assumed that the primary axis would take the per- 

 pendicular. Apparently, such was not always the case, to judge 

 from one or two instances, which have been discussed above. 



The discrepancies apparent in the figures between the marks on dif- 

 ferent days, especially in the upper hemisphere, are the results of differ- 



