DEVELOPMENT OF GEPHYREANS. 16r 
that of the Annulata. There is in Phascolosoma no true 
ovary, but the eggs float in masses in the capacious body- 
cavity, the animal being a hermaphrodite. 
Phoronis is from the highly developed crown of long, 
slender tentacles, and its complicated blood- -system, remark- 
ably like the Serpule, with which Annelids it is by some 
authors associated. The alimentary tube, however, is like 
that of Phascolosoma, the intestine folded and ending next. 
to the mouth. No nervous system has been detected. A. 
pulsating artery is attached to the upper side of the long 
cesophagus, and its branches go into the tentacles from an. 
cesophageal ring. ‘‘T'wo venous trunks open from the sin- 
uses above and behind the arterial branches, and then pro- 
ceed downwards, half encircling the csophagus, till they 
unite in a large vessel on its neural surface.” (Dyster.) 
This worm is minute, about four millimetres in length, and 
lives in a tube buried in holes in rocks. It has a strong re- 
semblance to a Polyzoon, but connects the Gephyrea with 
the true Annelids. 
In the Sipunculus-like worm Phascolosoma, and in Pho- 
ronis, there is a well-marked metamorphosis, and the larva: 
are somewhat like those of Annelids. The larva of Phas- 
colosoma is cylindrical, the head small, with a circle of cilia, 
but there are no arms as in the larva of the Phoronis. 
The earliest observed stage of Phoronis* is a free-swim- 
ming larva, the body transparent, ciliated, with an umbrella- 
like expansion on the head, covering the region of the mouth, 
while the end of the body is truncated. At this stage it is a 
true Cephalula, like that of Echinoderms and worms. Af- 
terwards four projections arise at the end of the body, and 
twelve long, arm-like projections grow out, the larval form. 
now being fully attained. In this condition it was de- 
scribed as a mature animal under the name Actinotrocha. 
When the Actinotrocha is about to transform into a Pho- 
ronis the end of the intestine bends up, opening outward 
*In our Outlines of Comparative Embryology this account of the 
metamorphosis of Phoronis is by mistake regarded as descriptive of 
Sipunculus on pp. 157, 158, under Development. The word Phoronis 
on those pages should be substituted for Sipunculus. 
