156 BRITISH SERPENTS. 
head, where subsequently the dark V-shaped mark 
is to appear, there is now a white V. That is to 
say, the pigment here has not yet been deposited, 
although the zigzag marking has been completed all 
alone the back. I have since observed this in: other 
embryos. The dark V seems the last mark to develop, 
as it is the most characteristic when developed. The 
Fic. 37.—Empryo ADDERS. 
white V is best seen in the middle embryo in the 
illustration last given. The allantois is seen in the 
embryo on the right, 
Up to this time I had no difficulty in- seeuring 
specimens to illustrate the adder’s development; but 
towards the end of August the females begin to retire 
into secluded spots, as before mentioned, and were 
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