Objects for the Microscope. 171 



PLUMULARIA FALCATA 



is another species, in which you may observe the polype 

 cells seated in close array along the pinnae of the branches ; 

 these, when dry, bend inwards like a sickle, and give the 

 name of Sickle Coralline to this zoophyte. It is dredged 

 in deep water, and common on oyster beds. A wavy branch 

 of it will not unfreqnently be found on the back of some old 

 crab, which has served as its perambulator, and carried it 

 into rich stores of Diatoms and Infusoria, such as it 

 delights in. 



POLYZOA 



GEMICELLARIA. 



This is one of the Polyzoa, more highly organized than 

 Sertularia, &c., and therefore ranking considerably higher 

 in the scale of creation. The difference in the skeleton 

 here prepared is, that we have a calcareous cell instead of a 

 horny one. Almost all the Polyzoa have calcareous sheaths, 

 or polyzoaries, as this skeleton is called, instead of poly- 

 pidom, which belongs to the lower class of zoophytes. The 

 difference between the two is this : a polypidom is a sepa- 

 rate horny case, which is formed before the indwelling and 

 connected polype, and the polype itself is part of a common 

 central mass, having a simple stomach, thread-like tenta- 

 culse, which seize food and draw it to the mouth, and 

 which multiply by ovarian vesicles containing medusoides. 

 The polyzoary is a case or tunic investing the body of a 

 distinct and separate polype, which is either horny or cal- 

 careous, sometimes forming a dense hard crust on stones 

 and shells. 



The polype within is quite different from that of the 

 Anthozoa. It has ciliated tentacles. The Polyzoa is a 

 part of the polype itself, investing it as a tunic or case, 

 which is sometimes horny, but most frequently calcareous, 

 even forming dense crusts upon shells, stones, or sea- weeds. 

 Though always found in a mass, the Polyzoa are strictly 

 solitary individuals, without inward connection, each polype 



