REPTILIA 577 



THE TURTLE 



The pond turtles of various genera belonging to Family Emydidae 

 have long been used as convenient and useful examples for studies 

 of reptilian characteristics. While there are many variations in 

 details, the main features of Troost's turtle, Pseudemys troostii 

 elegans (Wied), are foundj very little modified, in other members of 

 the family. This is one of the most abundant species of the Mississippi 

 Valley region and is veiy frequently the turtle sold by supply houses 

 for laboratory use. 



One of the most interesting characteristics of this species (P. 

 troostii elegans) has only recently been discovered. The adult males 

 are frequently melanistic; i.e., have the normal color pattern con- 

 cealed by a superimposed layer of black pigment. The 3'oung males 

 have the same coloration as the females and only gradually take on 

 the melanistic coloring. Hence, all stages from normal coloration to 

 jet black can be found among them. 



Habits and Behavior 



These turtles are commonly seen sunning themselves on logs 

 along the margins of ponds and rivers. When disturbed, they fall 

 into the water with a splash and swim hastily for the deeper parts 

 of the body of water. This activity in daylight hours might lead 

 one to suspect that they are entirely diurnal, but turtles are known 

 to feed at night. Hence, it seems that they are not as strictly regu- 

 lated by hours of light and darkness as are most vertebrates. Since 

 all turtles are cold-blooded animals, they hibernate in winter in 

 temperate regions. Turtles are often seen in considerable numbers 

 in a restricted localitj^ but there is no congregating or communal 

 instinct among them. Each one is totally oblivious of the presence 

 of all the others, except during the mating season, when the males 

 seek out the females. Turtles have been observed to mate at all 

 times from spring to autumn but the chief mating period occurs 

 soon after the animal comes out of hibernation in the spring. The 

 eggs are laid soon afterwards in a hole or pit in the earth excavated 

 by the female for that purpose. When the full complement has 

 been deposited, she covers them and returns to the water. Turtles 

 taken in the autumn months are often found to contain a full com- 

 plement of completely shelled eggs. This indicates that the mating 

 that commonly occurs immediately prior to the laying of these eggs 



