56 SQUIRTS, POLYPS, AND JELLY-FISHES. 
a peculiar sieve-like chamber—whose walls are 
made up of delicate vessels—into which food parti- 
cles are carried, and through which the admitted 
water passes into a second chamber, 
which also receives the alimentary 
canal. From this second chamber 
the water, which bathes the blood- 
vessels forming the meshes of the 
sieve-like respiratory sac, is expelled 
through the. second chimney-pot 
opening, and thus a constant circu- 
eae M,mouth;s, Jation is kept up. A remarkable 
“pilates age ei fact connected with the circulation 
of this animal is that the heart, 
which lies near the base of the respiratory sac, after 
beating a short time suddenly stops, and that with 
each renewal of action the direction of the blood- 
current is reversed. From the peculiar external 
tunic which encases the animal, the group to which 
the squirt belongs has been designated the Tuni- 
cata. 
A considerably larger form than Molgula is that 
which has received from fishermen the name of 
‘sea-peach’ (Cynthia), in allusion to the similarity 
in form and coloring existing between it and the 
peach. Other species of nearly identical structure 
and habit are the ‘sea-pears’ (Boltenia), which are 
supported on long slender stalks, measuring as 
much as a foot or more in length. These are almost 
invariably covered with foreign associations of plant 
and animal matter, presenting a coarse and untidy 
appearance. 
