452 



Kepoet of the State Geologist, 



The fresh-water form, Paludioella, and all marine forms have 

 the lophophore circular and the tentacles arranged in a single 

 row on its outer border, having, when expanded, somewhat the 

 form of an inverted cone. The tentacles are cylindrical, with a 

 blunted extremity. They are hollow and are composed of two 

 layers (fig. 23) ; the outer layer being composed of comparatively 

 large spherical cells, frequently with a brilliant nucleus, and the 

 inner layer of a very thin transparent membrane, without any 

 trace of a cellular structure. 



The exterior of the tentacles has two rows of vibratile cilia, 

 situated on opposite sides, one row vibrating toward the extremity 

 and the other toward the base. 



The tentacles are hollow and communicate with the perigastric 

 cavity through the lophophore. In all the Hippocrepian forms the 

 tentacles are surrounded, on their lower portion, by an exceed- 



t a 



Fig. 22. Lophopus cristatus. a, Tentacles; &, Calyx; c, Lophophore; d, Intestine; e, Invaginated 

 portion of the endocyst; /, Nerve ganglion; g, Nerve filament co lophophore; 7i., Nerve filament passing 

 around the lophophore ; i, Anus ; k, Epistome ; k', Orifice in lophophore forming a communication 

 between the cavity of the epistome and the perigastric space ; I, Elevator muscle of the epistome 

 (after Allman). 



