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D elami nation. In the late "blastula" stage, just before the 

 appearance of the dorsal lip, there is the following distribution of 

 pigment. Of the upper, pigmented, hemisphere, one side is con- 

 siderably darker than the other. Immediately beneath this darker 

 portion, the pigment extends for a short distance over the lower hemi- 

 sphere, forming (when the white pole is viewed) a light brown 

 crescentic area at one side of the egg. The dorsal lip of the blasto- 

 pore makes its appearance just beneath the light brown crescent. 

 Morgan and Tsuda ('93) make the statement that the dorsal lip 

 appears on that side of the egg, which (in the upper hemisphere) 

 is the lighter in color. Eycleshymer writing more recently ('98) 

 finds, as I do, that this is not the case. The distribution of pigment 

 may be most accurately learned by examining the black and white 

 poles of the same egg, using ordinary and inverted microscope — 

 or simply ordinary microscope, with the egg compressed between two 

 slides, turning the slides. 



If during the time (hour or two) immediately preceding the 

 appearance of the dorsal lip ^), the randzone be examined with a 

 ^/g inch objective, it may be seen that the white cells round the edge 

 of the zone are dividing and growing pigmented, while the light 

 brown cells of the zone itself are also dividing and growing more 

 pigmented. This is true of the whole randzone, both of the light 

 brown crescentic area below which the dorsal lip first appears, and 

 of the rest of the zone. After the appearance of the dorsal lip, this 

 division and pigmentation of cells (phenomenon may be styled de- 

 lamination) continues to go on in and round the edge of the re- 

 maining portion of the randzone, until the entire blastopore lip is 

 definitively established. With the appearance of the blastopore lip 

 in any region, the delamination comes to an end, the randzone by 

 this time having increased considerably in width through the in- 

 corporation of (the products of division of) the adjacent yolk cells. 



1) A convenient procedure for observing the first appearance of 

 the lip, and the phenomena preceding the appearance, is the following. 

 Divide a batch of eggs in the advanced blastula stage, putting some 

 in a comparatively cold room, keeping others at the ordinary working 

 temperature in a dish over a mirror. Examine latter at intervals, and 

 when the blastopore appears, select some eggs from those retarded by 

 the cold, compress and keep them under continuous observation until 

 appearance of lip. In compressing the egg, it should be rolled into a 

 position, where the part (region of dorsal, lateral, or ventral lip) to be 

 observed, is not too near the periphery. 



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