METAMORPHOSIS OF ACTINOTROCHA. 207 
have dropped off, and the short tentacles are directed straight 
forwards, and form a circlet surrounding the mouth. The 
posterior portion of the larval body (p.), with the anus at 
its extremity (q.), is still distinct, and is bent at right angles 
to the long axis of the pouch, which must now be called the 
body proper. In time it becomes bent still further upwards, 
and, at the same time, is gradually withdrawn into and fuses 
with the remainder of the body. Ultimately it quite dis- 
appears, and the anus remains as an opening on the side of 
the body, immediately behind the circlet of tentacles. 
Figure 13 represents 4 about twenty-four hours after the 
metamorphosis, when the larval body has completely fused 
with that of theadult. The body is soft and extensible, and, 
though it has numerous transverse folds when contracted, 
there is no indication of metamerism. The aboral extremity 
is extremely changeable in shape; two forms commonly 
assumed are shown. The surface is everywhere finely 
granular, and becomes distinctly tuberculose towards the 
aboral extremity. 
New tentacles are henceforward constantly budded forth 
at the dorsal side of the lophophore, at about the rate of a 
new pair every day, until their number becomes a hundred 
or more, and they increase gradually in length. 
Figure 14 represents the same individual as that shown 
in fig. 13 twenty-two days after metamorphosis, and practi- 
cally in the adult condition. The tentacles are richly 
ciliated, and have exactly the same appearance and perform 
the same movements asin the Polyzoa. Each has, however, 
a cecal vessel from the pseud-hemal circumoral ring, and 
performs a distinctly respiratory function. The pseud-hemal 
fluid is very remarkable from the presence of numerous 
large, oval, nucleated corpuscles, which look not very unlike 
the red corpuscles of frogs’ blood, though of less regular 
shape. They are also red in colour, and render all the 
branches of the pseud-hemal system very conspicuous, so 
that their arrangement may be very easily made out. In 
neither of the Chesapeake species is there a vessel run- 
ning along the intestine towards the anus, although such a 
vessel is figured by Metschnikoff. Norcan I agree with this 
observer that the corpuscles of the pseud-hzemal fluid are 
developed free in the perivisceral cavity to be drawn into the 
pseud-hemal vessels at the time of metamorphosis. There 
cannot be the least doubt that in both our species these cor- 
puscles are developed in solid masses adhering to the 
stomach walls, near the base of the tentacles, and I believe 
them to a rise within the cavity of a sinus, which becomes 
