216 HYATT, 



inner side, and its upper free border forms the true aper- 

 ture of the ccenrecial cell. This is shown by the position of 

 the sphincter muscle and its action in closing the cell, by 

 drawing together the upper edge of the calyx-like fold and 

 including the free ends of the tentacles which have been 

 previously bent inwards and doubled upon themselves.* 

 Thus not only does the so-called calyx homologize in po- 

 sition with the invaginated fold of the higher Polyzoa, 

 but it closely resembles that organ in function, with the 

 exception, however, of performing the office of a sheath 

 for the invaginated tentacles in the absence of any evag- 

 inable tube. Both Urnatella and Pedicellina are invag- 

 inated zooids, and as such cannot be associated with those 

 forms of Polyzoa which have the three regions of the 

 body fully differentiated. The lophophore is permanently 

 held attached to the inferior edge of the evaginated fold, 

 and cannot be extruded from the cell, the superior por- 

 tions of the tentacles being the only parts freely evagin- 

 ated. I am aware that Pedicellina is said to possess an 

 epistome and two arms by Prof. Allman, but these char- 

 acters will hardly weigh against the absence of the tubu- 

 lar endocyst, which" is common to all the Polyzoa from 

 the Cheilostomata to the Phylactolsemata, the absence of a 

 funiculus, and the simple character of the whole organiza- 

 tion. Their appearance, also, is more suggestive of the 

 Radiata than other Polyzoa, especially Urnatella, and the 

 peculiarity of permanent invagination is shared equally 

 with the young of the Phylactolaemata, whose lopho- 

 phores at an early age are permanently invaginated and 

 joined with the parietes of the cell, and are unfurnished 

 with cesophagal valves. Embryology, therefore, as well 

 as their general structure, justifies the position assigned 

 to them, as the lowest types of the Polyzoa. 



The concentration of the three regions is towards the 

 anterior end of the Polyzoon, and if I am right in my es- 

 timation, this is a low feature. The evagination of the 

 Perigastric and neural systems among the Cheilostomata, 



* This is most clearly shown by several of Dr. Leidy's figures in 

 which the tentacles are withdrawn as described. 



