

PREFACE 



In these " Outlines" the student is introduced to the study 

 of Chordate development through the embryological history 

 of Amphioxus. Whether or not Amphioxus represents a truly 

 primitive type of development, it affords, in simple diagram- 

 matic style, the essentials of early Chordate ontogeny. In 

 many respects the later phases of its history are highly modi- 

 fied, but this need be no objection to its use as an introductory 

 type, since it may serve immediately to put the student upon 

 his guard against a too exact phylogenetic interpretation of 

 embryological facts. 



Following this is a rather full account of the development 

 of the frog, a form that represents, better than any other single 

 type, what we may regard as the general type of Chordate 

 development. The chapters on the chick are relatively briefer 

 and emphasis is laid upon the embryonic membranes, and upon 

 the early phases of development, which represent the most 

 frequent modifications of the type of Chordate development, 

 modifications correlated with the presence of the large yolk 

 accumulation of the Sauropsid ovum. 



It is believed that the chapters on the frog and chick have 

 been written in such a way that either form may be omitted, 

 in a brief course of study. Or in case the study of the early 

 development of the frog is desired as a comparative introduc- 

 tion to the study of the embryology of the chick, Chapter III, 

 on the organogeny of the frog, may be omitted without serious 

 interruption of the continuity of such a course. 



The final chapter on the Mammal includes only those phases 

 of development that are of chief interest to the general student, 

 namely, the earlier stages in the formation of the embryo, 

 the establishment of its relation with the maternal organism, 

 the development of the embryonic membranes and appendages, 

 and the development of the external form of the human embryo. 



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