376 0. 0. WHITMAN. 



A Rare Form of the Blastoderm of the Chick, 

 and its Bearing on the Question of the For- 

 mation of the Vertebrate Embryo. 



By 



C. O. i;%'liit!nan, PIi.O. 



With Plates XXIV and XXV. 



In the summer of 1878, while in Leipsic, I obtained a blas- 

 toderm of the chick, Avhich presented at least one unusual and 

 very remarkable feature. The egg had been kept in an incu- 

 bator, at a temperature of 37° to 38° C, for eighteen hours. 

 After cutting away a portion of the shell and removing as 

 much of the white of the egg as could be done without injury 

 to the embryonic disc, the remainder of the egg, while still in 

 the shell, was carefully dropped into a bowel of nitric acid 

 (10%). The embryonic portion was then freed from the 

 coagulated white by the aid of a feather, and, after fifteen 

 minutes' immersion, was carefully cut around by sharp scissors 

 and floated into a watch-glass. The vitelline membrane was 

 then removed by the aid of pincers, and the yolk detached by 

 gently shaking the blastoderm in the watch-glass. The acid 

 was next turned off and replaced with distilled water, several 

 times renewed. After being thus thoroughly Avashed from the 

 acid it was stained in an aqueous solution of carmine, then 

 passed through several grades of alcohol, and finally mounted 

 in balsam. The whole process was accomplished without 

 causing any distortion or wrinkle, and without the loss of any 

 portion of the blastoderm, as the preparation still shows. 



