372 LEFEVRE. [Vou. XIV. 
In Pl. XXX, Fig. 6, is shown a transverse section of a 
stolon. The outer wall of the hollow cylindrical tube consists 
of a flattened epithelium, the ectoderm (ec.), covered externally 
by the transparent cellulose test (¢.). Running from one side to 
the other, the septum (/7.), is seen in cross-section, completely 
dividing the tube into two compartments or sinuses (d/.s.), in 
which the free cells of the blood lie scattered about. This 
stolonic partition consists of a double lamella made up of flat, 
attenuated cells, and may be described as a collapsed cylinder, 
the walls of which are closely pressed together and attached 
along the upper and lower borders to the inner surface of the 
ectodermal tube. It divides the stolon longitudinally into halves, 
and stretches entirely across the lumen, although in preserved 
material it is usually more or less shrunken away from the outer 
wall. The two compartments of the stolon are in open com- 
munication with the body cavities of the animals, so that a free 
circulation of blood occurs from one individual to another. 
As Kowalewsky (12) has pointed out, the partition (‘ Schei- 
dewand”’) does not reach quite to the extreme distal end of the 
stolon, but there the two spaces or sinuses open into each 
other. The blood flows in opposite directions in the two sides 
of the stolon, up one to the tip, around the free end of the 
partition, and down the other. When the heart beat is reversed, 
of course the direction of the blood flow in the stolon is changed. 
The buds always arise in the plane of the partition, on the 
side of the stolon opposite to that which is attached to the 
underlying surface; the line of attachment is, therefore, parallel 
to and immediately beneath the lower border of the partition. 
It will be seen further on that the definitive median plane of 
the bud coincides with the plane of the partition, and hence the 
latter structure divides the stolon into a right and left half in 
reference to the parts of the bud, and not into a dorsal and 
ventral portion, as described by Kowalewsky (12), whose well- 
known figure of the Perophora stolon is consequently mislead- 
ing. Looking at the lateral surface of the buds, as shown in 
that figure,! the partition would be seen from the flat side and 
not on edge. 
1 This figure is reproduced in Korschelt and Heider’s Extwicklungsgeschichte, 
p- 1366. 
