440 ZOOLOGY 
and form the posterior limit of the prebranchial zone (Fig. 
. 255.—Transverse section through 
© the branchial region of a Ciona intes- 
tinalis. After Roule. 
1. Atrial chamber. 8. Rectum. 
2. Branchial chamber. 9. Oviduct. 
3. Test. 10. Vas deferens. 
4, Mantle. 11. Ciliated endostyle. 
5. Vessel passing from a branchial bar 12. Branchial slit, stigma. 
into the mantle. 13. Branchial bar connected with mantle. 
6. Ventral blood-vessel at base of endo- 14. Muscle fibres. 
style. 15. Dorsal lamina. 
7. Dorsal blood-vessel at base of dorsal 
lamina, 
254). The anterior of these two ridges is the most pro- 
minent; it forms a simple circle; the posterior is, however, 
-Tr 
Fig. 256. 
A. Part of branchial sac of 
Ascidia from inside. 
B. Transverse section of same, “sg 
drawn to different scale. ons \V, a VEVAVAVAY: 
tr. Transverse vessel. O hei rn iia 
d. Connecting duct. aay fasta a 
hm. Horizontal membrane. 
° . . hm Crest 
il. Internal longitudinal bar, \ Ae 
lv. Fine longitudinal vessels. 
p, p'. Papillae. 
sg. Stigmata. 
continuous with the dorsal lamina, a structure which runs 
