PREFACE. 



The accompanying volume is designed primarily for the use of students taking 

 a practical laboratory course in embryology. It is intended to direct the student's 

 attention to actual, original observations, to be made by himself, and to aid him in 

 drawing correct conclusions from those observations. By this plan, the student re- 

 peats and uses the actual methods by which embryblogical science has been built. 

 If he pursues such a course diligently, he will be able at the end of it to say that 

 he knows of his own knowledge. To attain this result is the ideal of laboratory 

 education. 



In preparing .the new edition, advantage has been taken of the experience 

 gained with the use of the book by the author's classes, and of valuable sugges- 

 tions from many friends. The work has been so extensively revised that it may be 

 described as almost a new book. Chapters III to VI have been entirely recast and 

 rearranged so as to conform to the chronological order of development, an arrange- 

 ment which it is believed most readers will prefer to that adopted in the original 

 edition. Chapter II, on the early development of mammals, has been considerably 

 expanded; not with the object of giving a comprehensive treatment of the subject, 

 but rather with the intention of aiding the student to get, in connection with his 

 laboratory work, a connected story in his mind of the development of the principal 

 organs and systems of the body. Some new sections will be found also in Chap- 

 ter I. A considerable number of the figures are replaced by'new ones. The total 

 number of illustrations has increased from 218 to 262. With these changes it is 

 hoped that the second edition will deserve a continuance of the favor shown to 

 the original issue. 



The author takes much pleasure in acknowledging gratefully the invaluable as- 

 sistance afforded him by members of his laboratory staff, and wishes to call at- 

 tention especially to the very admirable original illustrations which have been fur- 

 nished especially for the book by Drs. J. L. Bremer, F. P. Johnson, F. T. Lewis, 

 R. E. Scammon, and F. W. Thyng. Special mention must be made also of the 

 figures from models made by Messrs. W. W. Behlow, G. C. Coe, L. M. Fergu- 

 son, C. A. Hedblom, and A. R. Kilgore, students in the" embryological course at 

 the Harvard Medical School. 



A large majority of the illustrations are from the Harvard Embryological Col- 

 lection, without which this work would not have been possible. The author requests 

 those who use this book to communicate to him any suggestions, which their 

 experience may lead to, for improving it. 



CHARLES S. MINOT. 



HARVARD MEDICAL SCHOOL, May 28, 1910. 



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