iv PEEFACE. 



for the first time, and are for this reason given rather 

 in extenso. 



As regards the illustrations, I am indebted to the 

 Koyal Society for the blocks of Figs. 17, 18, 20, and 21, 

 whilst Figs. 3, 6, 9, 16, 19, and 25 have been copied 

 from illustrations in their publications. Figs. 22, 23, 

 and 24 are copied from .Davenport's " Experimental 

 Morphology/ 7 and Figs. 7 and 8 from Bateson's " Ma- 

 terials for the Study of Variation." The rest are 

 either original, or from sources indicated in the text. 



I desire to take this opportunity of expressing my ob- 

 ligations to Mr. E. S. Goodrich for his kindness in read- 

 ing over the manuscript, and to Professors "W. F. R. 

 Weldon and S. H. Vines, for their useful advice and 

 suggestions. 



