CHAPTER X 



THE PEACTICAL STUDY OF THE EMBEYOLOGY OF 

 THE COMMON FOWL 



For gaining practical experience in the study of embryology there 

 is no type of material so convenient as that of the early stages in the 

 development of the Common Fowl. Freshly laid eggs can be obtained 

 practically anywhere and to obtain the various stages of development 

 all that is necessary 1 is to keep the eggs at a suitable temperature 

 (about 38° C.) either under a sitting hen, or in one of the incubators 

 which Can be purchased, or even in a simple water-jacketed oven 

 such as can be made by any tinsmith. If an incubator be purchased 

 it will be provided with a proper heat regulator for use with elec- 

 tricity, gas or oil, while with the most primitive water-bath it is 

 possible to arrange a lamp so as to give a temperature sufficiently 

 constant as to carry the eggs through at least the first few days of 

 incubation — the most important period for purposes of study. Bird 

 embryos — apart from their use in learning practical embryology — 

 provide admirable material for giving practice in the ordinary 

 methods of section-cutting which are in such constant use in Zoology, 

 Anatomy, Physiology, and Pathology. This chapter will then be 

 devoted to giving an account of the development of the Fowl with 

 directions as to the technique involved in its practical study. 



In the description which follows the developmental phenomena 

 will be described in their natural sequence but on account of the 

 practical difficulties involved in the extraction and preservation of 

 blastoderms of the first day of incubation it will be found best, in 

 actual laboratory work, after studying the new-laid egg and its 

 envelopes, to proceed to the stage of about 42 hours' incubation and 

 gain some practice in the manipulation of it before attempting the 

 earlier stages. In the following technical instructions the sequence 

 is followed which has been found to be in practice most convenient 

 for beginners. 



TECHNICAL DIRECTIONS 2 



I. New -Laid Egg. — Fill a glass vessel about 4| inches in 

 diameter and 2 inches in depth with normal salt solution [water 



1 Provided the eggs have been fertilized. 



2 The reader is assumed to have an elementary knowledge of the ordinary methods 

 of cutting sections. See, however, the Appendix. 



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