author's abstract of this paper issued 

 by the bibliographic service, januabt 19 



CUSHION CELLS OF THE PHARYNX OF PRORHYN- 

 CHUS APPLANATUS KENNEL 



WM. A. KEPNER AND W. J. SCOTT 



University of Virginia 



ONE TEXT FIGURE AND ONE PLATE 



A wide range of variability both in structure and function is 

 presented by the pharynx and proboscis of Rhabdocoela. Of 

 the seven famihes in this sub-order, the Catenulidae and Mi- 

 crostomidae have but simplex pharynges. In the Prorhyn- 

 chidae and Dalyelliidae, the pharynx is a well-defined bulbous 

 type. In the Typhloplanidae, there is a rosette-shaped pharynx; 

 in some of these, however, the proboscis lacks a definite sheath. 

 This proboscis is not concerned wdth ingesting food; but is an 

 organ of both defence and offense. This organ reaches its 

 highest development in the Polycystidae and Gyratricidae. 



Prorhynchus applanatus occupies an intermediate place in 

 this series of Rhabdocoeles, ranging from anmials having rela- 

 tively simple pharynges, through those presenting complex 

 pharynges without associated proboscides, to animals in which 

 both pharynges and highly developed proboscides are present. In 

 the simplest pharynx there is but little muscular development 

 and many glands present, so that, in the living specimen, the 

 pharynx appears to be a glandular structure rather than a mus- 

 cular one (e!g., Stenostoma). In the Dalyelliidae and irost 

 Prorhynchidae, the bulbous pharynx is highly muscular. The 

 pharynx of Prorhynchus applanatus is not only highly muscu- 

 lar, but its muscles are so organized that in the living specimen 

 three distinct zones are clearly recognizable, (text-fig. A). The 

 distal zone, {a) of muscles form an 'EndkegeF similar to the 

 terminal cone of such a highly specialized proboscis as that of 

 Gyratrix hermaphroditus Ehrenberg. At the posterior end of 

 the pharynx is a zone of muscles, comparable to the 'Muskel- 



475 



