THE OPINIONS OF NRO-LAMARCKIANS. 519 



In the same year, in discussing the origin of the 

 great development of the incisor teeth in the Roden- 

 tia, 1 Professor Ryder, in summing up, ventured "the 

 reflection that the more severe strains to which they 

 were subjected by enforced or intelligently assumed 

 changes of habit, were the initiatory agents in causing 

 them to assume their present forms, such forms as 

 were best adapted to resist the greatest strains with- 

 out breaking." In 1878 the writer 2 advanced the fol- 

 lowing proposition : "Change of structure is seen to 

 take place in accordance with the mechanical effect of 

 three kinds of motion, viz., by friction, pressure, and 

 strain." In the same year Professor Ryder went into a 

 discussion of the specific application of strains in the 

 evolution of the dental types of the diplarthrous Un- 

 gulata, and prepared the field for work in the Rodentia 

 and Proboscidia. 3 In 1879 the writer gave mechan- 

 ical reasons for the reduction of the sectorial teeth of 

 Carnivora to one, and for their present position in the 

 jaws. 4 In 1881 the writer 6 described the specific ac- 

 tion of impacts and strains in the production of the 

 existing characters of the articulations of the limbs in 

 the higher Mammalia. In 1887 the same subject, to- 

 gether with that of the mechanical origin of the char- 

 acters of the molar teeth, was more fully investigated 

 in a paper on the Perissodactyla. 6 In 1888 the writer 

 published a paper on the mechanical origin of the sec- 

 torial teeth of the Carnivora, 7 one on the mechanical 



1 Proceeds. Phila. Acad., 1877, p. 318. 



2 American Naturalist, January, 1878. Origin of the Fittest, p. 354. 

 3 Proceeds. Phila. Acad., 1878, p. 45. 



4 American Naturalist, -March, 1879. 



5 American Naturalist, April and June, 1881. 



6 American Naturalist, 1887, pp. 985, 1060. 



7 Read before the American Association for the Advancement of Science, 

 New York, 1887, p. 254. 



