io| EXPERIMENTAL EVOLUTION LECT. 



Pouchet l says : " Balaenidae certainly are among 

 those higher vertebrates whose skeleton exhibits 

 least fixity ; this is a peculiarity which cannot be 

 denied." The same writer also says that in many 

 species which live in limited regions the same skeletal 

 variability exists in a marked degree, and although 

 the individuals are absolutely similar so far as exterior 

 characters are considered, they may display a varia- 

 bility which may be said to be unlimited, in the 

 number and relations of the bones. And Pouchet and 

 Beauregard 2 say also that it would prove difficult 

 to meet with two skeletons of the Anteater which 

 were exactly similar as concerns the number of the 

 ribs or vertebrae, or the connections of the ilium or 

 ischium with the vertebral column. 



As to differences in weight and length of the skeleton 

 in different individuals of the same species, Darwin 

 and Wallace have also collected numerous data of 

 which all are cognizant. The soft parts of the body 

 display the same tendency. All have heard of John 

 Hunter's experiments on the sea-gull (Lams tridacty- 

 lus}. He fed it during a year on grain, with the result 

 of hardening to a large extent the inner coat of the 



1 A propos de deux Photographies de Baleine Franc he. Compt. Rend, 

 Soc. Biologie, 1890, p. 705. 



- Traite d? Osteologie Comfaree, 1889, p. xii. 



