380. Report of the Microscopical Section. [Sess. 
organ, still forced along by ciliary action, till they reach 
the cesophagus, whence they pass into the stomach. Here 
they are subjected to the usual processes which fit them for 
nourishment, while the refuse passes along the intestinal canal 
into the atrial cavity, whence it is ejected along with the water 
through the atrial aperture. The soluble parts of the food 
which have been fitted for nourishment pass through the wall 
of the intestine into the small blood spaces, and are thus con- ' 
veyed to all parts of the animal. 
The heart or seat of the circulation of the blood is merely a 
delicate, slightly enlarged tube, lying behind the stomach. It 
has no valves, and is connected at its ventral end with the 
great ventral blood-vessel running alongside the endostyle,: 
and at its dorsal end with the great dorsal blood-vessel 
running alongside the dorsal lamina. As has been noted, 
these two large blood-vessels are connected with each other’ 
by a circular vessel which runs round the neck of the 
branchial sac behind the peripharyngeal bands. They are 
also connected with the transverse and interstigmatic vessels, 
and from them connectives are also given off to the body-wall 
and test, so that a complete system of circulation is constituted. 
The blood thus leaving the ventral end of the heart passes 
into the great ventral blood-vessel, and is thence distributed 
into all the smaller blood channels, and as it passes through 
these in the wall of the branchial sac it comes into close 
proximity with the water passing through the stigmata, and 
thus receives its supply of fresh oxygen, and returns purified 
by the dorsal vessel to the heart. 
A peculiarity in the circulation of the blood in the Ascidia 
is that it is not continuous in one direction. Its flow from 
the ventral end slackens, and then stops, when the flow com- 
mences in the opposite direction. This change in the direction 
of the flow takes place every minute or two. The cause 
of this curious phenomenon is thought to be the blood being 
forced into the smaller vessels in greater volume than can get 
through, so that they become engorged, and ultimately force 
back the blood, thus causing a reversal in its flow. 
The Ascidia is hermaphrodite,—that is, it possesses both male 
and female reproductive organs. These lie close together on 
the left side of the body alongside the stomach and intestine,’ 
