ON A PRORHTNOHID TURBELLARIAN. 635 



parenchyma is apparently syncytial, with a coarse reticulum 

 continuous from cell to cell, and large nuclei. Strands of 

 muscular fibres (parenchyma muscle) pass through it, mainly 

 in a dorso-ventral direction. 



No account is given by v, GrafF^ or by Vejdovsky ^ of the 

 integument in Prorhynchus, so that I have no means of 

 comparing it with that of the form under consideration. The 

 superficial integumentary glands apparently correspond to the 

 cells described by Vejdovsky (I.e., p. 144) as occurring on the 

 ventral surface of P. hygrophilus, and figured in fig. 76. 



Digestive System. — The pharynx (fig. I, ph.) is of great 

 relative size (about one third of the entire body in length) and 

 high degree of complexity. It is capable, as shown in one of 

 the specimens, of protrusion to some extent through the 

 aperture of the mouth, when the free margin appears irre- 

 gularly lobed. Its sheath extends back only a short distance 

 from its anterior end. Its form is that of a thick-walled, 

 cylinder somewhat contracted posteriorly. The layers of 

 muscle in its wall (fig. 4) have the following arrangement, 

 taken from without inwards: — (1) External longitudinal, (2) 

 external circular, (3) internal circular, (4) internal longi- 

 tudinal. Between the external and internal circular layers is 

 a broad zone occupied only by glands, nerves, and radial and 

 arched fibres. The radiating fibres run from the inner surface 

 of the external longitudinal layer to the basement membrane ; 

 they divide the internal longitudinal layer (which lies imme- 

 diately beneath the epithelium and basement membrane) into 

 numerous very regularly arranged bundles. The arched fibres 

 are all directed in the transverse plane, so that they only 

 appear in transverse sections. They are arranged in bundles 

 running with a strong curvature from the external circular 

 layer to the deeper part of the internal circular. The pharyn- 

 geal unicellular glands lodged in the zone above referred to 

 send narrow ducts inwards to open into the internal cavity of 



» 'Monographic der Turbellarien,' I. " Bhabdoccelida," p. 264 (1882). 

 ' " Zur vergleichenden Auatomie der Turbellarein," ' Zeitsclir. f. wiss. 

 Zool.,' Ix (1891). 



