216 



ence in size is iindoubtedl}' greater than is indicated in the sections, 

 since in the surface views of compressed eggs, the cells forming 

 the upper edge of the dorsal lip may be seen to be much longer 

 than they are wide, and thus they are cut in the sections in the 

 direction of their greatest length. The furrow which frequently is 

 rounded (probably the first condition), is in places slightly angular 

 (Fig, 8 a), or irregular (Fig. 8 b). At the bottom of such a furrow, 

 small gaps (g in Fig. 8 b) may frequently be found between the cells, 

 the gap being apparently filled with pigment, though I believe an 

 actual space exists between the cells (this is indicated by the sharp- 

 ness of the line of pigment, which bounds the gap — the sections 

 not being especially thin. 



~^—i 



Vig. 8. Three median longitudinal sections (a, b, c) through the region of the dorsal 

 lip, of Chiirophilus gastrulas, in the very earliest stages of gastrulation. Camera, Zeiss D 2. 

 In a, the very shallow blastopore furrow, b. /., is angular in section. In b, the furrow 

 is irregular in section. lu c (a thick section), the blastopore furrow at successive levels 

 of the section is siiown at 1', 2', 3'. The furrow in places, as at 1' and 2', exhibits 

 sharp depressions. 



These gaps I take to be the representatives of the intercellular 

 pigment spots, seen in surface view (Fig. 3), while the shallow furrow 

 itself ecapes notice in this view. Again in sections through the 

 stage, where the dorsal lip has but just appeared, the furrow fre- 

 quently exhibits sharp depressions Ijung between cells obliquely in- 

 clined to one another, and with the oblique surfaces heavily pig- 

 mented. Such a depression is shown in Fig. 8 c, which represents 

 a very thick section, the edge of which at successively lower levels 

 is indicated by the lines 1, 2, 3, the deepest parts of the furrow at 



