AtTTHOR'S ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, JANUARY 19 



PHARYNX OF IVIICROSTOMA CAUDATUM 



WM. A. KEPNER AND FRANK HELVESTINE, JR. 



University of Virginia 



ONE TEXT FIGURE AND THREE PLATES 



Microstomum caudatum is frequently confused with Steno- 

 stoma leucops. The sexually immature individuals of these gen- 

 era greatly resemble each other. The chief differences lie in 

 their alimentary canals. The alimentarj^ canal of Microstoma 

 caudatum consists of two regions — the enteron and the stomo- 

 daeum. The elongated, sac-like enteron extends anteriorly over 

 the dorsal side of the pharynx (fig. 1, B, and fig. 6, A.S.). This 

 blind end or caecum of the enteron, lying over and projecting 

 beyond the pharynx, constituted the chief diagnostic feature of 

 ^Microstoma caudatum. The stomodaeum is represented by a 

 short, glandular-walled tube — the pharynx (fig. I, A). This is a 

 simplex pharynx. It is rather more highly refractive than the 

 other organs of the body and can, therefore, be readily recog- 

 nized as the animal turns on its side or back. It is not definitely 

 limited by a membrane, so that its glands stand out discrete pro- 

 jecting into the surrounding mesenchyme (fig. 1, ^4). When a 

 sexually mature specimen lies on its back in a hanging drop, two 

 openings of the body are conspicuous on the midline. One of 

 these, the female genital pore, lies at the anterior limit of the 

 posterior third of the body (fig. 1, C) ; the other, the mouth of 

 the pharynx, lies at the posterior limit of the anterior fifth of 

 the body (fig. 1, M). Von Graff ('09) describes and depicts 

 the mouth as a longitudinal, slit-like opening but suggests no 

 other details. Alartin ('08) shows in his figure 10, plate 14, an 

 open mouth, guarded by a circular disc-like lip. This is the near- 

 est approach of any student to our observation of the details of 

 this mouth. A living specimen, caught resting dorsal side down 



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JOURNAL OF MORPHOLOGY, VOL. 33, NO. 2 



