MICHIGAN ACADEMY OF SCIENCE. 101 



Variation due to Age. 



It is a well known fact that many characters change considerably with age. For in- 

 stance the young of the blue racer is banded on the back with brown, so that to the super- 

 ficial observer it resembles a young water snake. At this stage it is very different from 

 the older specimens. The relative measurements also vary quite noticeably. In order 

 to establish a standard by which young and adult blue racers could readily be classified it 

 was arbitrarilv determined to consider all snakes under 1200mm. in length as young and 

 all over that limit as adult. Working on this basis it was found that there was a marked 

 difference in the relative length of head in young and adults. The young blue racers have 

 a head .04 % of body length, while the adults have a head per cent only .025, a difference 

 of .015 %. Seven specimens just out of the eggs were interesting in this connection. 

 They have an average head % of .051, or more than twice as much in proportion to body 

 length as adults. Tail length shows a slight variation. The young have a tail % of .238 

 and adults .235, a verv slight indication that in young blue racers the tail % is greater 

 than in the adults. The seven specimens from ithe egg show an average tail % of .24, 

 .002% more than all the young averaged together, and .005 % greater than the adults, 

 indicating that up to adult life the proportion of tail length to body length gradually be- 

 comes less. 



The Difference due to Sex. ~ ■^ 1 



The difference due to sex are surprisingly slight. Adult males show an average length 

 of 1466mm. and females 1343mm. showing that males are .09 % longer than females. The 

 head % of adult males and females is the same (.025%) and although the figures at hand 

 give young males a head % of .36, and females .044, there is reason to believe that a 

 larger number of specimens will show that no such disparity exists. The great apparent 

 difference here is due to the fact that the larger proportion of very voung snakes hap- 

 pened to be females. The male tail %. of .234 is a trifle less (.003) than the female of .237%. 



In the matter of gastrosteges and urosteges the same surprising similarity between 

 the sexes appear. Adult males and females average 184 and 181 gastrosteges respectively 

 with ranges of 175-192 and 171-189. Males average 89 urosteges with a range of 78-98, 

 and females average 84 with a range of 73-93. -This difference in the number of urosteges 

 was hardly to be expected when the close agreement of the sexes in tail % was taken into 

 consideration. But like other blue racer variations due to sexes it is so small, that a larger 

 number of specimens may increase the similarity. Curious variations were showTi by 

 individuals. One had two half plates (gastrosteges) interpolated on opposite sides and 

 the first five gastrosteges of another were divided. The most interesting specimen in 

 this connection however was a large female which had 15 gastrosteges divided and 15 uros- 

 teges undivided. 



Twenty-six out of thirty-five males have their upper labials normal (7-7) four have 

 8 on one side, one has 75-7, one 6J-65, one 7-6J, one 6-7, and one very large specimen 

 (1601mm.) had only 6-5. Of the twenty-three females 17 are normal, 4 have 8 on one side 

 and two have 6 on one side. .743% of the male are normal and .735% of the females, 

 again emphasizing the close agreement in the sexes of blue racers. 



The tabulation of lower labials in the spring of 1903 was made on the basis of 9-9, that 

 is, counting the seven large plates — 4 before and two after the fifth and largest, and also 

 counting the two small scales that are under the vipper labials. Examination by Dr. 

 Clark and myself of the thirtv-eight specimens captured that spring led us to the belief 

 that the 7-7 large plates are the normal lower labials and in 1904 the presence or absence 

 of these alone, was recorded. 



Of the 22 males captured in 1903 16 have 9-9 lower labials, 5 have 8 on one side and one 

 has 8-8. Of the 13 males taken in 1904, 12 were regular, having the 7-7 large lower 

 labials, and one remarkable specimen, the same large male (1601mm.) before cited as 

 having 6-5 upper labials, had only 5-5 lower labials. 



The 16 females of 1903 show more variation than the males, 11 have 9-9 lower labials, 

 3 have 8 on one side, and 2 have 8-8. Six of the seven females of 1904 have 7-7 and one 

 has 6-7. 



Summing up: 89% of the males are found to be normal, and 70 % of the females. 



Thirty-four of the thirty-five males had the normal number (2-2) of post-oculars, and 

 had 3-2. One had 2 labials on each side, one had 2-2 pre-oculars, one had 2-1 pre-oculars 

 and one had 6-6 temporals. 



The twentv-three females all had 2-2 post -oculars. One had a sub-loreal on the left. ' 



97 % of the males and all the females were therefore regular in the number of post- 

 oculars. 11 % of the males varied in the matter of pre-oculars or loreals, and only 6 % 



