104 INTRODUCTION TO POLYZOA. 



distinct body-cavity, and the individuals are 

 unisexual instead of bisexual, as in the 

 Polyzoa. 



PHRONIDEA and BRACHIOPODA. 



Above the Polyzoa in point of structure 

 the PHYLA PHRONIDEA and BRACHIOPODA, 

 are placed. In these, the chief point to be 

 noted is the modification of the tentacle-arms, 

 which are coiled up and supported by an 

 internal shelly skeleton. In addition to being 

 organs of touch, they also subserve aeration. 

 In the BRACHIOPODA there is a ventral and 

 dorsal shell, and the animals are never 

 compound. 



MOLLUSCA. When the Polyzoa are 

 compared with the Mollusca proper, it is found 

 that the latter, with their well-formed heart, 

 extensive nervous system, and several other 

 features, are so far in advance that the gap is 

 remarkable. It can hardly be doubted, 

 however, that there are in the lamellar gills, 

 and foot of the bivalve mollusc, the homologues, 

 respectively of the tentacular crown, and the 



epistome of the Polyzoa. 



P. J. E. 



