CHORDATA 439 
the genital ducts run for some distance along the dorsal 
middle line, and with these runs the dorsal blood-vessel. 
The walls of the branchial sac are also connected with the 
mantle at irregular intervals by blood-vessels, which pass from 
the bars to supply the substance of the mantle. The branchial 
bars run at right angles to one another, and leave between 
them small ciliated slits or stigmata, through which the water 
taken in at the mouth escapes into the peribranchial chamber, 
the current being maintained by the cilia. The transverse 
bars contain blood-vessels communicating with the dorsal 
and ventral blood-vessels. Connecting two adjacent transverse 
bars are a number of small longitudinal bars, which divide the 
space up into the stigmata. There are two kinds of transverse 
bars, the primary and the secondary, the latter being the 
smaller. In addition to the small longitudinal bars, there are 
also some large ones situated in a different plane from the 
others, farther inside the branchial sac; these are connected 
by a short vessel with the transverse bars at their points of 
intersection (Fig. 256), and at the same spot they give off 
little finger-shaped processes, which hang into the lumen of 
the sac. 
A ciliated groove, known as the hypopharyngeal groove or 
endostyle, runs along the ventral line of the branchial sac 
(Fig. 254). The lips of the groove project into the cavity 
of the sac, and it is lined by cells which are partly glandular 
and partly ciliated. At the posterior end it is continued into 
a cul-de-sac, which has a slight spiral twist ; anteriorly its lips 
are continuous with the peripharyngeal bands, two ciliated 
ridges which encircle the anterior end of the branchial sac 
7. Stomach. 16. Heart. 
8. Intestine showing typhlosole, part 17. Ovary. 
of it removed to show subjacent 18. Pore of vas deferens. The openings 
structures. of the oviduct and the vas deferens 
9. Rectum. are shown enlarged to the right. 
10. Anus. 19. Testicular follicles on intestine; the 
11. Atrial aperture. greater part of them have been 
12. Inner surface of mantle, showing removed with the intestine. 
longitudinal and transverse muscle 20. Oviduct. 
fibres. 21. Septum shutting off that part of 
13. Dorsal tubercle. the body-cavity which contains 
14. Subneural gland and brain. the heart, stomach, and generative 
15. Cut edge of branchial sac. organs. 
