THE LANGELET. 
139 
The mouth is oval, surrounded with a circle of ciliated 
tentacles supported by semi-cartilaginous processes arising 
from a circumoral ring. The mouth leads directly into a 
large broad phaiTiix or '^brancliial sac" (Fig. 183,^), pro- 
tected at the entrance by a number of minute ciliated lobes. 
The walls of this sac are i)erforated by long ciliated slits, 
comparable with those of the branchial sacs of Ascidians 
and of Balanoglossus. The water which enters the mouth 
passes out through these slits where it oxygenates the blood, 
and enters the peribranchial cavitj^, thence passing out of 
the body through the abdominal pore (Fig. 183, p). The 
pharynx leads to the stomach (/), with which is connected 
the liver or coecum. There is a pulsatile vessel or tubular 
Fig. 183.— vent; /, stomach; g, pharynx; n, nervous cord; p, pore; r, noto- 
cord; ^, tentacles. From Liitken's Zoology. 
heart, beginning at the free end of the liver, and ex- 
tending along the under side of the pharynx, sending 
branches to the sac and the two anterior branches to the 
dorsal aorta. ^^On the dorsal side of the pharynx the 
blood is poured by the two anterior trunks, and by the 
branchial veins which carry away the aerated blood from 
the branchial bars, into a great longitudinal trunk or 
dorsal aorta, by which it is distributed throughout the 
body." (Huxley.) There are also vessels distributed to 
the liver, and returning vessels, representing the portal 
and hepatic veins. The blood-corpuscles are white and 
nucleated. 
The vertebral column is represented by a notocord 
which extends to the end of the head far in front of the 
nervous cord; and also by a series of small semi- cartilagin- 
ous bodies above the nervous system, and which are thought 
to represent either neural spines or fin-rays. The nervous 
cord lies over the notocord; it is not divided into a true 
