i66 ARCHICCELOMATA. 



Ba/anoglossus is an important type of the Archicoelomata 

 and is additionally interesting as having in its anatomy a 

 foreshadowing of certain organs found in the Chordata (see 

 Char data). 



It belongs to the Archicoelomata, chiefly because of its 

 archimeric segmentation of the mesoderm and the Archi- 

 chorda from the presence of chordoid structures and pharyn- 

 geal clefts. 



III.— LOPHOPUS. 



Phylum - - - Archicollomata (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 lophophore 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 

 bein<4 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 epistoine, 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 polype retracts itself and fhe tentacles are withdrawn. 



In the interior of the animal we find that the mouth leads to an 

 oesophagus 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 coelom 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 tra?7sverse septtwi. 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 \hQ 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 ox funiadiis which 

 attaches the alimentary canal to the aboral end and a retractor mwsclQ runs 

 beside it. The mesoderm upon the funiculus gives rise to testes and 

 ovaries and the animal is her7n aphrodite. The main nerve-ganglion 



