360 



MISS JOAN B. PROCTER ON THE NUMBER OF 



diately behind the head, the drop to 21 rows taking place by the 

 termination of series Y. at about the level of the 15th ventral. 

 This series is in course of development, and in several specimens 

 it crops up on the middle third of the body to a degree varying 

 from a single scale to a complete row, which, though it commences 

 by cropping up in an intermittent manner on this region of the 

 body of some individuals, develops and progresses both forwards 

 and backwards in others, and in one specimen unites Avitli its 

 originated portion on the neck giving tliis snake 23 uninterrupted 

 rows for more than half its length. This progressive development 

 of series Y., which in V. herus does not ever continue beyond the 

 anterior two-thirds of the body, evidently continues in species 

 having 25 or more scale-rows. 

 21-19. 



The second pair of series in course of development is the lYth. 

 In normal specimens which have 21 rows of scales this series 

 terminates about two-thirds down the body, nsually by fusing 

 with tho Illrd. In specimens which have 19 rows instead of 21 

 it is only present on the neck ; its development from this point 

 taking place in precisely the same manner as that of series Y 

 19-17. 



The first pair of series in course of reduction is that next to the 

 vertebral ; ita termination takes place on the third quarter of the 



Text-figui'e 3. 



Vipera herns, dorsal view, to show termination of series IV. on left side, fusion of 

 series IV. with III. on right side, and termination of the pemiltimate series 

 on both sides, frds down the body. 



body usually two-thirds down. In the normal Yiper, which has 

 21 rows of scales on its anterior two-thirds, this point almost 



