BIGELOW. Development of Leoas. 



PLATE 10. 



Figures from sections. Ventral side (blastopore) at the left in figures of sagit- 

 tal sections, and at the lower side in figures of transverse sections. Blastoderm 

 one cell in thickness. 



Fig. 87. Sagittal section of a stage with two hundred and fifty cells (estimated). 

 The mesoblast band (ras'W.) is extending anteriorly along the dorsal 

 side. 



Fig. 88. Sagittal section of a later succeeding stage. Egg has elongated posteri- 

 orly. Continued extension of the mesoblast. 



Figs. 89, 90. Transverse sections through an egg similar to the one represented 

 in Figtre 88 and made at the levels indicated in that figure by the 

 numbers 89 and 90. Mesoblast dorsal in Figure 90. 



Fig. 91. Sagittal section of later stage. Two transverse dorsal furrows (1, %} 

 mark off the three metameres. Compare with Figure 122. 



Fig. 92. Transverse section of egg in same stage as that of Figure 91, showing 

 the median dorsal longitudinal furrow. The mesoblast has greatly 

 thickened and extended ventrally on either side of the entoblast. Com- 

 pare with Figure 90. 



Fig. 93. Sagittal section of still later stage. Two new transverse furrows (3,4) 

 partially subdivide the first and third metameres of the previous stage. 

 Compare with Figures 123-125. 



Fig. 94. Transverse section of stage similar to that shown in Figure 93. Longi- 

 tudinal furrow extending laterally and ventrally folding off the 

 appendages, in which process the transverse furrows 1-4 share 



