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cases however particular cells in the region where the ventral lip 

 later makes its appearance, were kept under observation for an hour 

 or more (they are seen very obliquely); and they underwent no ap- 

 parent change in position, although they divided. I select a particular 

 case for description. The egg was placed in position at 12 M., and 

 the dorsal lip appeared as a slightly curved line, close to periphery 

 of the image at 1 P.M. Previously to the appearance of the dorsal 

 lip, there was visible round the periphery of the egg, a very narrow 

 and irregular border of pale brown cells — the rest of the under 

 surface was white, and without "chromatophores". By the time 

 the dorsal lip has appeared, the region directly above (external to) 

 it, is a distinct brown. Elsewhere round the egg periphery, a few 

 chromatophores and isolated faintly brown cells have made their 

 appearance, at a little distance from the egg edge and within a region 

 which at 12 M. was white. By 2 P.M. the dorsal lip is distinctly 

 curved, and perceptibly wider (if the egg diameter be put at 100, the 

 chord of the lip is 65); and it has moved inwards a short distance 

 from the periphery towards the centre of the image. By this time 

 there is visible round the remaining part of the egg periphery, a 

 zone of considerable width, vaguely marked off from the inner white 

 mass by a variable degree of pigmentation. Round the extreme peri- 

 phery of the zone there is now, as at 12 M., a narrow irregular 

 border of a distinct brown color, and from this run inwards certain 

 irregular brownish projections (areas made up each of a considerable 

 number of cells), which were visible at 12 M. in the same 

 position which they now occupy. The rest of the zone shows 

 abundant chromatophores, but the cell bodies including them exhibit, 

 for the most part, in this light (cells viewed obliquely) scarcely a trace 

 of color. Here and there in the zone may be seen isolated cells or 

 small groups of cells, of a distinct brown tint. Thus between 12 M. 

 and 2 P.M., chromatophores and some distinctly brownish cells have 

 appeared in the peripheral region of the white area, and have spread 

 towards the centre of that area. In this chromatophore zone (zone 

 of delamination), the size of the cells diminishes considerably between 

 12 M. and 2 P.M. By 4 P.M. the dorsal lip has been extended, until it 

 now includes something less than half a circle, and it has moved still 

 further from the periphery towards the centre of the image. The 

 delaniination zone round the rest of the periphery is of about the 

 same width as at 2 P.M., but is much more distinct. The cell bodies 

 of the zone all have now a slight brownish tinge, some tracts of cells 

 being much darker than others; and the chromatophores are darker 



