370 



BERTRAM G. SMITH 



first cleavage, in two others the median plane is at right angles to 

 the plane of first cleavage, while in the five remaining eggs the 

 median plane is obUque to the plane of first cleavage: a result 

 that is about what we might expect if the relation between these 

 two planes is held to be purely a matter of chance. 



3. Staining experiments, A method of making permanent 

 marks with Nile-blue sulphate on the hving egg of Crypto- 

 branchus has been described in a previous paper (Smith, '14). 

 Since the stain is slightly toxic, certain precautions must be 



Figs. 12 and 13 Equatorial views of two eggs of Cryptobranchus alleghenien- 

 sis in advanced segmentation stages, showing the biradial character of the cleav- 

 age pattern in the lower hemispheres. Fig. 12, stage 8; fig 13, stage 9. The 

 figures were drawn with the aid of a camera lucida. X 7. 



observed. The egg is removed from its accessory egg envelope, 

 but retains the chorion (the structural equivalent of the vitelline 

 membrane of the frog's egg). The egg is then immersed in 

 water in a Syracuse watch-glass, and a rather strong aqueous 

 solution of the stain appHed with a capillary pipette in such a 

 manner as to make the smallest possible distinct spot. After 

 about thirty seconds the excess of stain is removed with a pipette 

 of larger caliber and the dish flooded with fresh water. Not more 

 than one egg is placed in each watch-glass, and the water is 

 changed several times during the first day, and once a day there- 

 after. With few exceptions, eggs so treated develop normally. 



