yiii PKEFACE. 



siderable detail, and the descriptions are mainly from my own 

 observations. In the study of the placenta, especially in its 

 earlier stages, I have been greatly helped by D aval's careful 

 investigations. 



In the chapter dealing with the Human Embryo I have been 

 compelled to obtain my material almost entirely from the obser- 

 vations of others ; and notably from the splendid and long- 

 continued work of Professor His, to whom it is due that our 

 knowledge of human embryology is in so many respects more 

 precise than that of any other mammal. It is a source of great 

 regret to me that my friend Professor Minot's important treatise 

 on Human Embryology only came into my hands while the last 

 sheets of my own book were passing through the press, and that 

 I have been unable to avail myself of the rich store of facts, and 

 of the numerous suggestive explanations which his work con- 

 tains. 



A large proportion of the figures are new, and have been 

 made expressly for this book from my own drawings. In the 

 new figures, as well as in a large number of those which I have 

 copied from the works of others, I have adopted, so far as 

 practicable, a uniform mode of treatment and of lettering, which 

 will, I hope, facilitate comparison of the figures of the several 

 types with one another. I am under great obligations to the 

 publishers of the works from which figures have been borrowed, 

 for permission to reproduce these ; and more especially to 

 Messrs. Vogel, of Leipzig, for their ready consent to supply 

 electrotypes, and to allow a large number of figures to be copied 

 from Professor His' great monograph on the development of 

 the Human Embryo ; a courteous liberality that is not always 

 to be met with in this country. 



I wish also to record my indebtedness to my friends Dr. 

 Robinson and Mr. Assheton for many valuable suggestions and 

 criticisms in the course of the work, and for much kind assist- 

 ance in the correction of the proofs. To Mr. P. Hundley and 

 Mr. G. Pearson, by whom the drawings on the wood were made, 

 and the blocks engraved, my thanks are due for the great care 



