AMPHIBIA, REPTILES, OTHER CHORDATES 95 



median organs, such as the nostrils. Instances are 

 known of the occurrence of four nostrils, representing an 

 even slighter degree of twinning than the presence of a 

 third or median eye in fishes. 



Gemmill (191 2) cites a 

 case of a three-headed snake 

 seen near Lake Ontario by 

 Bruch. He also notes that 

 another three-headed snake 

 was reported by Andro- 

 vandus from the Pyrenees 

 Mountains. 



Among Chelonia there 

 are very few recorded in- 

 stances of twinning. Bate- 

 son describes and figures an 

 interesting specimen of two- 

 headed tortoise (Fig. 45) in 

 which the heads behaved independently as though they 

 had distinct individualities. Such a creature might have 

 some difficulty in deciding on a direction of locomotion. 

 This is, so far as I know, the only recorded case of twin- 

 ning among the turtles, but I am convinced that embry- 

 onic twinning is not infrequent. While living for some 

 years on Lake Maxinkuckee in Indiana, a lake plentifully 

 stocked with several species of turtles, I took occasion 

 to study this group in a rather intensive fashion. Among 

 other things studied were the breeding and nesting habits 

 and the general features of the embryology. Many a 

 morning expedition was made to watch the turtles building 

 their nests in the sand and in soil of various characters. 

 Most of the species dig out with their hind feet a vertical 



Fig. 45. — Double monster 

 turtle of the anadidymus type. 

 (After Bateson.) 



