180 THE ANIMAL KINGDOM. 



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 

 being perfect in itself, and distinguished from the Anthozoa 

 by that of its ciliated tentacles, which do not seize the prey, 

 but create currents in the water whereby food is carried 

 into the mouth. 



This is a great distinction, and must be observed, of 

 course, in the living animal ; a very curious sight it is to 

 watch the shoals of little golden fish-like naviculse whirled 

 into the vortex of a hungry polype, the currents running 

 along the cilia or delicate fringe which edges each tentacle. 

 Some polyps have two stomachs, one a kind of gizzard, 

 triturating the food, and the other digesting and discharging 

 the refuse. There is even a rudimentary liver a valve at 

 the pyloric opening ; the stomach itself is lined with cilia ; 

 in short, the living polype you are now looking at in 

 its dead state was a wonderfully organized little creature, 

 though scarcely visible to the naked eye. Instead of the 

 ovarian vesicles of the Anthozoa we find, especially on 

 Mustra and Lepralia, little pearly cells, which are gemmse, 

 or buds, thrown forth from the body of the polype. They 

 have two methods of propagation, one by gemmation, the 

 other by a true sexual generation. (See f Carpenter on the 

 Microscope/ p. 575.) 



