172 WM. A. KEPNER AND W. H. TALIAFERRO 



SUMMARY 



1) Correlated with the absence of a chitmous penis, which in 

 the other forms of Prorhynchus is used as an organ of defense, 

 the pharynx of Prorhynchus applanatus serves as a defensive 

 structure. 



2) The four organs of special sense of Prorhynchus applanatus 

 are always composed of a definite number of cells (viz., eighteen) 

 each of the two eyes is formed by two cells and each of the two 

 ciliated pits by seven cells. 



3) The simple eye of Prorhynchus applanatus differs from that 

 of Planaria torva, as described by Hesse, only in that the visual 

 cell of the former presents a highly refractive lens-shaped por- 

 tion of cytoplasm at the base of the rhabdome. 



4) The ciliated pit of Prorhynchus applanatus is sharply differ- 

 entiated into three regions: sensory, accessory, and glandular. 



5) The ciliated pit of the thigmotactic rhabdocoele, Pro- 

 rhynchus applanatus, differs from that of a free swimming form, 

 like Microstoma caudatum, in having a musculature by which 

 the pit may be lifted from the substratum. 



6) The affinity between the Turbellaria and the Nemertini, 

 which was suggested by the structure of the ciliated pits of 

 Microstoma caudatum, is further strengthened by the more 

 highly specialized ciliated pit of Prorhynchus applanatus. 



