44 WM - A - KEPNER A^D W. H. TALIAFERRO. 



the unicellular glands of the pharynx, but which has its cells 

 resting directly upon a transverse commissure connecting the ven- 

 tral, lateral nerves (text-figures I and 2, TVand Fig. 3, N). Martin 

 ('08, Fig. 10) has shown how the pharynx of Microstoma caudatum 

 Ldy. is everted when about to ingest a Hydra. In a similar way 

 we have seen Microstoma caudatum Ldy. evert its pharynx in 

 testing the edible or non-edible quality of plants and debris about 

 which it was swimming. Judging from the intimate morpho- 

 logical relation between this band of pharyngeal cells and the 

 nerve commissure and the manner in which the pharynx is 

 operated, we believe we have here a primitive gustatory organ. 



The ventral nerves in passing along the right and left sides 

 of the pharynx might have made similar contacts with the 

 pharyngeal epithelium and thus the gustatory organs would have 

 been in this case bilaterally arranged, but in such case they would 

 not be directed at right angles to what is the usual source of 

 stimulus due to the animal moving anteriorly and to the food 

 falling upon the floor of the pharynx. Thus we find this very 

 primitive gustatory organ, in a free-moving bilaterally sym- 

 metrical animal, to be a median structure. 



The ciliated pit when closed is a club-shaped sac which rides 

 the dorsal, lateral nerves (text-figure I, CP). Its lumen is lined 

 with cilia much stronger than the cilia of the general surface. 

 These are especially heavy near the mouth of the pit. The 

 ciliated columnar cells of the ventral side near the mouth lie 

 in intimate contact with the dorsal, lateral nerve (Fig. 4, DN). 

 Hence we consider them to be the peculiar sensory cells of the 

 ciliated pit, though we can see no other striking difference between 

 them and the other ciliated cells of the outer half of the pit. 

 Men have always looked upon these structures as being organs 

 of special sense. It is important to state in this connection that 

 here we have the same habit as the pharynx displays of repeatedly 

 exposing the sensory cells to contact with stimuli by opening and 

 closing the pit and the same kind of nerve supply as we have in 

 the median gustatory epithelium of the pharynx. Their reason 

 for being bilaterally placed is suggested in the latter part of this 

 paper. 



The epithelium of the ciliated pit, just as that of the pharynx, 



