No. 3-] BUDDING IN PEROPHORA. 409 
are attached in many places to the inner surface of the ecto- 
derm and outer surface of the endoderm, but that they are not 
more numerous at any one spot than another (Pl. XXX, Figs. 
7, 8). Their power of amoeboid movement over any surface 
with which they come in contact would account for their 
presence on the walls of the vesicles. 
It would seem more probable that these cells are all alike 
and indifferent, and that the nature of the organs to which they 
give rise is determined, not by any prearranged condition of 
their idioplasm, but by the particular point to which they 
happen to become attached. I regard it as a significant fact 
that cells are found, not only at the places where organs will 
arise, but also at many other points. Those of the cells which 
chance to fall, as it were, on fertile soil will undergo further 
development, and, under the formative influence exerted upon 
them by that portion of the wall to which they adhere, will be 
utilized in building up a definite structure. 
All parts of the walls cannot possess a specific determining 
power, and such cells as lodge on barren ground are not 
further modified, and do not furnish material for the formation 
of organs. 
According to this view, one of these cells is the equivalent of 
any other, and it is only a few that find favorable positions and 
have their latent possibilities called forth. Those which be- 
come attached at a point high up on the right side of the inner 
vesicle in the posterior region of the bud will form the pericar- 
dium; others on the dorsal side, at the anterior end, will give 
rise to the dorsal tube, and still others, which lodge on the 
upper wall of the latter, will help to construct the ganglion; 
some adhere to the inner surface of the ectoderm, lengthen out, 
and become muscle fibers; some wander through the ectoderm, 
and on the external surface are transformed into the cells of 
the cellulose test; while others find a definite place in the 
posterior region of the bud and develop into the sexual organs. 
This view is opposed to the supposition of Seeliger spoken 
of above, that in Clavelina the ganglion of the bud is formed 
from free cells of the blood which had earlier composed the 
larval ganglion and been liberated on the dissolution of that 
