166 ARCHICELOMATA. 
Balanoglossus is an important type of the Archicalomata 
and is additionally interesting as having in its anatomy a 
foreshadowing of certain organs found in the Chordata (see 
Chordata). 
It belongs to the Archicalomata, chiefly because of its 
archimeric segmentation of the mesoderm and the Azchi- 
chorda from the presence of chordoid structures and pharyn- 
geal clefts. 
III._LOPHOPUS. 
PHYLUM ARCHICCELOMATA (p. 170). 
SuB-PHYLUM BrYOZOA (p. 177). 
Lophopus is a small freshwater organism common in rivers and 
streams. It is a colony of individuals or polypes which are embedded 
in a common gelatinous investment. The whole colony executes slow 
creeping movements. 
Each individual has a crown of tentacles or /ophophore which is in 
the form of a horseshoe. It bears a row of tentacles the whole way 
round the edge of the horseshoe, the row on the outer or convex edge 
being continuous round the ends with that on the inner or concave edge. 
A web unites the bases of the tentacles. In the centre of the horse- 
shoe, between the rows of the tentacles, is situated the mouth. This is 
overhung by a small flap or process, the egzstome, between it and the 
inner row of tentacles. In the concavity of the lophophore, and hence 
outside the tentacles, opens the anus. When undisturbed, the animal 
spreads the tentacles apart and the cilia covering them cause currents 
with food-particles to pass towards the mouth. _—On stimulation the 
polype retracts itself and the tentacles are withdrawn. os 
In the interior of the animal we find that the mouth leads to an 
cesophagus and a lobular stomach, from which the intestine runs forward 
to the anus. The whole alimentary canal is therefore flexed into a U. 
The ectoderm is simple and secretes the gelatinous investment. 
Between it and the alimentary canal is the spacious ccelom lined by 
mesoderm. In the epistome is a pre-oral portion, the epistomial 
cavity, which communicates on either side with a lophophoral cavity 
produced out into each arm of the horseshoe and separated from the 
spacious trunk-cavity by a ¢ransverse septum. The trunk-cavity is lined 
by a thin layer of mesoderm which extends over the alimentary canal 
and inside the ectoderm. At the aboral end it is differentiated into 
circular muscles called the parietal muscles. These on contraction com- 
press the coelomic fluid and force the oral part of the polype upwards. 
From the base of the stomach there runs a band or fznzculus which 
attaches the alimentary canal to the aboral end and a refractor muscle runs 
beside it. The mesoderm upon the funiculus gives rise to testes and 
ovaries and the animal is hermaphrodite. The main nerve-ganglion 
