156 BRITISH SERPENTS. 



head, where subsequently tlie 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 

 along 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 



Fig. 37. — Embryo 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 securing 

 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 



