NO. 2020. VARIATION OF THE HIBAKARl SNAKE— THOMPSON. 



159 



The climate of continental islands is regularly milder than that of 

 the adjoining mainland of the same latitude. Where the range of 

 a species extends over regions that differ, in one having a more tem- 

 perate climate, the animals inhabiting the warmer are prone to be 

 the larger. The lengthening of the tail in this species is evidently 

 an example of this phenomenon. 



The increase in the length of the vertebral column has been con- 

 fined strictly to the caudal region. There has been no change in 

 the relative position of the internal organs. The gastrostege level 

 at which the principal viscera are situated may be presented in a 



table. 



Gastrostege level of the principal viscera. 



An inspection of this table brings to light the fact that where one 

 specimen has a few more body vertebrae than another the increase 

 has taken place in a definite part of the colunm. This region is 

 between the gall bladder and the ileo-caecal valve, and would corre- 

 spond to the lumbar region in the higher animals. 



The scales are in 19 rows anteriorly and 17 posteriorly; the IV 

 row is the one that is suppressed, and it terminates at the upper 

 half of an enlarged scale in the row below. 



Gastrostege level at xvhidi the suppressed rows terminate. 



At present there are only a few records of mainland specimens 

 but these are sufficient to show that there exists a marked tendency 

 toward a reduction in the number of head shields. The island 



