476 EVCLESHYMER. [Vou. XIV. 
In those amphibian eggs which are deeply pigmented, an 
eccentric distribution of the pigment has been noted by a 
number of investigators. Professor Whitman, in lectures on 
vertebrate embryology, has repeatedly called attention to the 
unequal distribution of pigment in the amphibian egg, and 
emphasized its importance in the orientation of the embryo. 
Morgan and Tsuda (Quar. Journ. Micr. Scz., 1894, p. 377) found 
an unequal distribution of pigment in the eggs of Rana, which 
they described as follows: “In all the eggs, from the earliest 
stages up to the blastopore, there is one marked peculiarity of 
the pigment. There is always a greater deposit of pigment on 
one side of the egg than on the other. ..”’ (p. 380). ‘The inter- 
esting point in connection with the two opposite, the darker 
and lighter sides of the eggs, on which I have dwelt at such 
length, is that the less densely pigmented half of the egg very 
early in the segmentation shows signs of a more rapid develop- 
ment and growth than the darker and pigmented side...” 
(p. 381). ‘The blastopore makes its first appearance on the less 
pigmented and further developed side of the egg.” My obser- 
vations on the eggs of Amblystoma (/ourn. of Morph., 1895, 
p. 367) led to the following conclusion: “In all the eggs where 
the differences are sufficiently marked to admit of orientation, 
the irregular line (blastopore) lies beneath the darker portion 
and is parallel with its more sharply defined border. It will be 
recalled that the deeply pigmented area is the area in which 
cell division has become much accelerated.” 
It is obvious that the conclusions of Morgan and Tsuda and 
my own, concerning the distribution of pigment, are at vari- 
ance. As to the position of the secondary area of cell activity, 
however, there is complete agreement. Assheton has also 
described this area. He states that: “ Possibly the secondary 
area of proliferation may start immediately upon the formation 
of the dorsal lip of the blastopore, and not delay until the 
whole blastoporic rim is completed.’ While there are minor 
differences of opinion as to the extent and time of origin of this 
area, there is no question as to its location or significance. The 
experiments recorded under III seem to show that this area gives 
rise to the greater portion of the posterior half of the embryo. 
