224 HYATT, 



essentially from those on the coenoecium, except in being 

 greater or less than the latter, as mentioned above, and in 

 having the power of expanding and contracting their pa- 

 rietes. They may swell to twice or three times the normal 

 size, and contract again with considerable quickness, as if 

 they had collapsed after parting with their fluid contents. 

 From the evaginable endocyst they can be followed into 

 the calyx, which, in the adult, is merely a web like fold of 

 the first membranous layer; and from the calyx into the 

 external ciliated membrane of the tentacles. 



The cells on the calyx and tentacles are of about the 

 same size as those on the evaginable endocyst, but they are 

 not so distinctly hexagonal, unless contracted. The outer 

 sides are more convex, than those on the coenoecium ; tbis 

 peculiarity is, also, shared by the cells of the evaginable 

 endocyst. The nucleus is large and brilliant. The nucleo- 

 lus was not defined. The cilia are prolongations of the 

 walls of the cells; each cell bearing one long slender hair 

 (Fig. 6). 



FIG. 0, two living cells, with cilia, from near the tip of a tentacle of FKEDERICELLA 

 REGINA. 



The vibrations of "the cilia are not constant, and, if a 

 tentacle be severed and quickly placed under the micro- 

 scope, those that are at rest can be viewed without diffi- 

 culty throughout their entire length. 



The cells become smaller on the lophophore, forming a 

 denser layer than on the other parts of the zooid. There 

 is no break upon the edge of the oesophagus and the cells 

 of the first membrane are continuous with the cells of the 

 innermost layer of the alimentary canal. 



(2) The second layer is made up of smaller cells. It is 



