er . 



In Fig. 6, Is sho-^n a transverse section of a sto- 

 lon. The outer wall of trie hollow cylindrical tube consists 

 of a flattened epitheliini, the ectoderm, ^ct., covered exter- 

 nally by the transparent cellulose test, _t. Running from 

 one side to the other the partition-wall, p_. t . , is seen in 

 cross-section, completely dividing the tube into two com- 

 partments, in which the free cells of the blood lie scattered 

 about. The 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 usual- 

 ly more or less shrunken away from the outer wall. The two 

 compartments of the stolon are in open communication with the 

 body cavities of the animals, so that a free circulation of 

 blood occurs from one individual to another. 



As Kov;alev;sky (12) has pointed out, the partition- 

 wall ( "Scheidewand ") does not reach quite to the extreme dis- 

 tal end of the stolon, but there the two spaces or sinuses 

 open into each other. The blood flows in opposite direction; 

 in the two sides of the stolon, up one to the tip, around the 

 free end of the partition, and down the otner. v/hen the 

 heart-beat is reversed, of course the direction of the blood- 

 flovf in tne stolon is changed. 



•8- 



