805 
within the membrane in the early stages or change its orientation 
with respect to the marks on the egg membrane. In order to mark 
the eggs they were removed from the water and partially dried. A 
needle covered with finely divided carmine was drawn horizontally 
over the eggs. Small particles of carmine stuck to the membrane in 
many cases. The eggs were returned to the water and the best marked 
chosen. 
Attempts to modify the cleavage by compression, shaking, removal 
of yolk, solutions etc. gave no results that need be recorded here. In 
the Fundulus-egg very many modifications are brought about by these 
means and will be described below. 
Orientation of Embryo. 
The carmine method of orientation was tried in order to deter- 
mine the position of the embryo on the egg. Thirty-one such observ- 
ations were recorded. They point unmistakably to the conclusion 
that as soon as the head end becomes definitely established it remains 
as a fixed point and the embryo increases in length entirely behind 
. this region. This statement needs qualification. If the carmine lay 
exactly in the center of the blastoderm at the time of first appearance 
of the germ-ring, the head end of the embryo very rapidly extended 
forward to the central point of the earlier blastoderm, but after reaching 
that point remained fixed relatively to the carmine throughout the 
later changes of development. In other words the head end of the 
embryo corresponds to the apex of the early blastoderm and when 
this point is reached it is retained. At about this time the blasto- 
derm begins to assume an excentric position to the vertical, moving 
forward. The carmine marking the center of the early blastoderm 
moves forward at the same rate. As the embryo appears and leng- 
thens the carmine continues to move forward together with a similar 
movement of the head end of the embryo, until at the time of closure 
of the blastopore both carmine and head end appear at the horizon 
of the egg. This forward rotation of embryo and membrane is with- 
out doubt caused by new adjustments of the growing embryo to its 
center of gravity. Owing to the close adherence of the embryo to its 
membrane the two revolve together; after the closure of the blasto- 
pore the embryo gradually looses its adhesion to the membrane. 
This rotation of egg and membrane of the pelagic fish-egg has so far 
as I know been overlooked and this has lead in one case to a serious 
mistake, In the sea-bass the oil globule remains always at or near 
the upper point of the egg. Inasmuch as the embryo rotates for- 
ward during its early period of elongation the posterior end remains 
