vi PREFACE 



also be made of the amphibian group (figure 10), drawn by Miss 

 Lisbeth Krause of the Osborn Laboratory staff, which is of the 

 same high quality. 



It is a pleasure to have another opportunity to acknowledge 

 the help received from my colleagues at Yale University, from 

 Professor W. B. Unger of Dartmouth College, and, in particular, 

 from Professor Woodruff, to whom I am also under great obligation 

 for his critical reading of the complete proof. In connection with 

 the new illustrations, especial mention should be made of the 

 assistance given by Professors S. C. Ball, W. B. Coe, B. G. Harri- 

 son, A. Petrunkevitch, L. L. Woodruff, and Dr. T. C. Barnes of 

 this laboratory ; also by Professor B. S. Lull, Director of the 

 Peabody Museum, and Professor G. B. Wieland, of the Depart- 

 ment of Botany, Yale University. Grateful acknowledgment is 

 also given to the American Museum of Natural History of New 

 York for assistance given to Mr. Harrison in connection with the 

 habitat groups shown in figure 4 and figure 9 ; and to the Mac- 

 millan Company for their permission to include figure 12 from 

 Needham's Chemical Embryology. Once more I am indebted to 

 the Macmillan Company for the interest shown in this work and 

 the splendid cooperation given which has made possible its prompt 

 publication. 



George A. Baitsell. 

 Osborn Zoological Laboratory 

 Yale University 

 April, 1932 



