MERISTIC VARIATION 39 



SECTION II MERISTIC VARIATION IN LINEAR SERIES 



Vertebrae. Among fishes and snakes variation in the number 

 of vertebrae may be very great. In mammals it is smaller but 

 yet distinct, as in the following examples, instances of which, 

 according to Bateson, could be multiplied indefinitely. 



ERINACEOUS EUROP^EUS (THE HEDGEHOG) 1 



It will be noticed that I and 5 differ only in the dorsal region, 

 which fact, however, affects the total, but that 4 and 8 differ both 

 in the sacral and the coccygeal without affecting the total. 



Commenting on the phenomena of an additional lumbar or 

 sacral vertebra, Bateson says : 



. . . There is a strong suggestion that (in cases of this kind) the num- 

 ber of vertebrae has been increased by simple addition of a new segment 

 behind, after the fashion of a growing worm ; the variation of vertebras 

 thus seems a simple thing. But there is evidence of other kinds, which 

 plainly shows this view of the matter to be quite inadequate. 



What this evidence is he proceeds to show by succeeding 

 examples, a few of which are reproduced here : 



In a skeleton of Pythott tigris^ (No. 602, Museum of the College 

 of Surgeons] the vertebrae are normal up to the I47th inclusive. 

 The 1 48th and i4Qth are, however, abnormally short from front 

 to back, suggesting arrested development with imperfect separa- 

 tion, although each vertebra bears a normal rib on either side. 



1 Bateson, Materials, etc., p. 103. 2 Ibid. pp. 103-105. 



