DEVELOPMENT OF SPELERPES BILINEATUS 



225 



pearance of the stained spots. Next afternoon there was still no 

 change in the marks when viewed from above, but on inverting 

 the egg, a remarkable series of changes had occurred. Fig. 50 

 is a view of the blastopore side of the egg. The equator is to be 

 thought of as passing near the centre of the drawing. Fig. 49 

 shows the opposite side, while fig. 51 shows the lower hemisphere 

 only. In figs. 50 and 51, marks A, D, F, and E, have become 

 elongated bands and extend into the blastopore, while B and C 

 (figs. 49-51) have elongated toward it. Nearly twenty-four hours 



Figs. 48-55 



later, viz., May 12, 4:30 p.m., (figs. 52 and 53) further changes of 

 like nature have occurred. E and F are little, if any, longer 

 than on the previous day, although at the blastopore ends, they 

 are closer together (compare fig. 51 with 53). The same lack of 

 elongation is true of A and D (fig. 53) . A has swung around so 

 that it now enters the blastopore from the lower side. F now 

 enters the blastopore at the corner. The blastopore has under- 

 gone considerable changes in shape, which will be discussed in 

 another place. Great changes have taken place in B and C. 

 They have elongated and now extend into the lower side of the 

 blastopore. As in earlier stages, all bands are conspicuously 

 narrower towards their blastopore end. They are somewhat 



