Gastriilatioii in the Pigeon's Ec-ff. 69 



&&• 



In most cg'gs the attaclmicnt of tlic cbalaza to the membrane 

 at the pointed end of the egg is much more intimate than at the 

 opposite end. This, together with the fact that the position of the 

 embryo upon the bhistoderm is constant, has led the writer to believe 

 that the chahiza3 phij an important role in maintaining the orienta- 

 tion of the egg in the oviduct. It seems very probable that the 

 place for the attachment of the chalazse to the vitelline membrane, 

 nt least at the small end of the egg, is determined in the ovary. ''^ 



From what has just been said it is obvious that eggs with ab- 

 normal chalazse can be used neither for experimental work nor for 

 sections, because the plane of section can not be determined. Con- 

 sequently the utmost care has been taken in this work to detect and 

 discard such eggs. 



Special attention has been given to methods and means of ex- 

 perimentation, for it became increasingly apparent as the work 

 progressed that there was need of a much more refined technique 

 than that used by previous workers in this field. I have, in steriliza- 

 tion and in opening and closing the window in the shell, employed, 

 in the main, the methods described in a previous paper (Patterson, 

 '07, a), and they therefore need little explanation. A one tenth 

 per cent solution of bichloride of mercury is used for sterilizing 

 all instruments, except the operating needle, which is sterilized 

 in alcohol. The wandow in the shell is made by the aid of a fine 

 pair of forceps, and after the operation is performed, this opening 

 is sealed with a piece of shell from a fresh egg, and a piece of 

 sterilized cotton is placed over the closed window. The egg is then 

 revolved until it is completely inverted, and thus, as the yolk turns, 

 the blastoderm is brought uppermost into a nonnal environment. 

 "Control" eggs show that by this method, not only is infection re- 

 <luced to the minimum but also that the retardation in development 

 which ordinarily accompanies this kind of work, is greatly reduced. 

 After the operated egg has been developed for the desired time, it 

 is taken from the incubator and the upper half of the shell removed. 

 This allows one to determine the relation existing between the axis 



'The writer has made observations and experiments to determine tliis point, 

 but as yet they are incomplete. 



