PKEFACE. 



IN this volume we offer to the public the first part of what 

 we hope may serve as a systematic introduction to the study 

 of Embryology. Some apology is perhaps necessary for the 

 separate publication of a part only of the whole subject; but 

 we trust that the following reasons will justify the course we 

 have adopted. 



Those who have paid attention to recent embryological 

 researches must be aware of what we may venture to call 

 the tumultuous condition of many parts of the subject, and 

 of the extreme difficulty in many cases of forming a clear 

 and decided judgment without the aid of independent 

 observations. It is this necessity of having repeatedly to 

 work over contested points with a view to reconcile 

 diametrically opposed .statements, or to verify startling 

 announcements, which has rendered so laborious the task 

 we have undertaken, and which so much delays its com- 

 pletion. 



On the other hand, whoever wishes to have a sound 

 foundation of embryological knowledge cannot do better 

 than gain a thorough insight into the development of the 

 bird. The practical advantages offered by the hen's egg 



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