142 GERM-CELL CYCLE IN ANIMALS 
(3) The nuclei of the vitellophags resemble the 
early cleavage nuclei; they are midway between 
the other two kinds in size, and their chromatin is in 
a more diffuse condition. 
Whether these three kinds of nuclei were all 
potentially alike before their differentiation is an 
important question. Visibly they are all similar 
until they become localized in definite regions of 
the egg, and associated with particular cytoplasmic 
elements. One cannot help but conclude that they 
were all potentially alike and that their differentia- 
tion was brought about through the influence of 
the cytoplasm in which they happened to become 
embedded. The writer has shown (Hegner, 1911a) 
that if the posterior end of a freshly laid egg of 
Leptinotarsa decemlineata is killed with a hot needle, 
thus preventing the pole-disc granules and surround- 
ing cytoplasm from taking part in development, no 
primordial germ cells will be produced. A large 
series of similar experiments have also proved that 
at the time of deposition, ‘“‘ The areas of the peripheral 
layer of cytoplasm (Fig. 36 khAbl.) are already set 
aside for the production of particular parts of the 
embryo, and if the areas are killed, the parts of the 
embryo to which they were destined to give rise 
will not appear. Likewise, areas of the blastoderm 
are destined to produce certain particular parts of 
the embryo” (Hegner, 191lla, p. 251). What 
becomes of the nuclei that are prevented from enter- 
ing the injured region of the egg? No evidence 
has been discovered to indicate that they disinte- 
