AUTHOR'S PKEFACE 



TO THE FIRST EDITION. 



" Die Entwickeluugsgesohiotite ist der wahre Lichttrager fur Untersnohungen 

 liber organische Kbrper." — C. E. v Baee, "Ueber Entwiokelungsgeschichte 

 derThiere"(Bd. I., S. 231). 



The Embryology of Animals, although one of the youngest shoots 

 of morphological research, has, nevertheless, grown up in the course 

 of sixty years, along with the cell-doctrine and that of the tissues, to 

 a vigorous and stately tree. The comprehension of the structure of 

 organisms has been extended in a high degree by numerous develop- 

 mental investigations. The study of the human hody has also derived 

 great advantage from the Same. In the newer anatomical text- 

 books (Gegbnbaur, Schwalbe) Embryology is receiving more and 

 more attention in the description of the separate systems of organs. 

 To what extent many things may be more clearly and attractively 

 described in this manner is best shown by a comparison of the des- 

 criptions of brain, eye, heart, etc., in the older and the more recent 

 anatomical text-books. 



Although it is generally recognised that Embryology constitutes " a 

 foundation-stone of our comprehension of organic forms," neverthe- 

 less the attention which its importance warrants is not yet given to 

 it ; it is especially true that it has not become as extensively as it 

 should be a component of well-rounded medical and natural-history 

 instruction, to which it is indispensable. The cause of this is 

 perhaps in part to be sought in the fact that in student-circles the 

 study of Embryology is often held to be especially difficult and a 

 comprehension of it to be laborious. And thus many do not venture 

 into this apparently obscure realm. 



But ought the development of an organism to be really more 

 difficult to comprehend than the complicated finished structure ? 



To a certain extent this was the case at a time when the most 

 divergent and contradictory opinions prevailed concerning many of 

 the most important processes of development, such as the formation 

 of the germ-layers, the protovertebrse, etc., which the lecturer had to 



