218 THE STUDY OF ANIMAL LIFE CHAP, xi 



alternate gripping and muscular engulfing, and the intact 

 egg slips into the gullet. It is then met by the sharp 

 points of the inferior spines of a number of the vertebrae, 

 which project into the gullet, and cut the egg-shells. 

 It is said that they are actually tipped with enamel. 

 The result of the structural adaptation is that none of 

 the precious egg is wasted. Mr. Ditmars, the Curator of 

 Reptiles at the Zoological Park in New York, who has a 

 wide experience of living snakes, says that the empty 

 egg-shells are always returned, and that this habit is 

 quite unique. 



The student is strongly advised to make a practical 

 study of some structures, such as a sheep's heart, a 

 bullock's eye, a dog's skull, a bird's skeleton, the appen- 

 dages of a crayfish, the lantern of a sea-urchin, in order 

 to become convinced of the intricacy and finish of adap- 

 tations. We have taken the bird's skeleton as an illus- 

 tration (Fig. 59). 



