176 MICHIGAN ACADEMY OF SCIENCE. 



early summer, the majority are found near the ponds and brooks as water 

 is an essential feature of the molting. Most of the snakes collected were 

 taken near the ponds and streams which are abundant in the vicinity of 

 Olivet. One hundred and forty-eight individuals were collected and the 

 following observations made on each one; sex, length of head, length of 

 tail, total length, number of gastrosteges, number of urosteges, number 

 of upper and lower labials on each side, maximum number of scale-rows 

 and color. The first topic which comes up for consideration is 



THE DIFFERENCES DUE TO AGE. 



Any one who has given attention to the subject of variation will have 

 noticed that many of the features change very markedly during the 

 transition from the younger to the older stage. Relative measurements 

 for instance, vary quite noticeably. Having to make some arbitrary 

 distinction for a comparison, I said that all snakes under 400mm. in 

 length were young, while those over 750mm. were old. Tabulating upon 

 this basis the relative length of head and tail it was found that in the 

 younger snakes both were slightly longer than in the adults. In the 

 young snakes the tail was twenty-two per cent, of the total length, while 

 in the older snakes it was 21.3 per cent, of the length, a difference of .7 

 per cent. The head was also relatively longer in the younger individuals. 

 In these specimens the head was 4.5 per cent, of the body length, while 

 in the adults it was only 3.3 per cent., a difference of 1.2 per cent., show- 

 ing that the greatest per cent, of growth between the two extremes of 

 age takes place in the bod}' proper. 



THE DIFFERENCES DUE TO SEX 



Were much more marked and much more interesting. After a little ex- 

 perience one can tell the sex of the snake by the external appearance 

 alone, with little danger of mistake. The female is, as a rule, much 

 thicker and more solid than the male and, in maturity, longer. Nearly 

 all the snakes over 750mm. in length and all of those over 800mm. were 

 females. The tail of the female is also relatively shorter, and one can 

 usually tell at a glance, whether his specimen is male or female by this 

 difference. Of the 148 individuals examined, sixty-three were males, and 

 in these specimens the tail averaged 23.3 per cent, of the total length, 

 while in the female it averaged 20.9 per cent., a difference of 2.4 per 

 cent, of the total length. It was interesting to note in connection with 

 this observation that there was no single point that marked the divid- 

 ing line between the two sexes, but that the minimum male and the 

 maximum female overlapped considerably. In connection with this in- 

 creased length of tail in the male the statistics showed that this differ- 

 ence was not accompanied by increased width of the urosteges or tail 

 plates, but by increased number. In the males the number of pairs of 

 urosteges varied from 65-81 giving an average of seventy-three, while in 

 the female it ranged from 57-71 with an average of sixty-four, giving the 

 male approximately nine more pairs of urosteges than the female. Com- 

 parison also showed, as we should expect, that in each sex there was a 

 very marked correlation between the number of urosteges and the rela- 

 tive length of tail. 



