MAKIM ZOOLOGY. 



Sub-Kingdom IV. MOLLUSCA. 

 Class I. POLYZOA. 



It lias "been usual, in our systematic books on 

 Zoology, to include the Polyzoa (or Bryozoa, as 

 tliey are sometimes termed) in tlie Class Zoophyta. 

 And truly, if we considered only their general ex- 

 ternal appearance, this would seem their most natural 

 alliance. Universally of microscopic minuteness, 

 growing parasitically on submerged foreign bodies, 

 as shells, rocks, and sea-weeds, springing (most of 

 them at least) from a creeping root-thread, in the 

 form of a tiny shrub, composed of successive series 

 of pellucid cells, from which protrude animals, each 

 surmounted by a coronet of radiating tentacles, all 

 connected organically in a compound life, — these 

 creatures do present, it must be confessed, very 

 many characters in common with the Sertulariadce 

 and other Hydroid Polypes. 



Yet when we examine the animals themselves, 

 we find them organized on a much higher type 

 than the Polypes, viz., on that which exists in the 

 Mussel and the Oyster, though in its most simple 

 condition of development. If we take one of 

 the calcareous-celled species, Scii]paria cJielata, for 



B 



29127 



