478 WM. A. KEPNER AND W. J. SCOTT 



the proboscis and the enteron. This connection between the 

 enteron and the vigorously active pharynx must be quite delicate ; 

 for there is but a verj^ thin tunic of muscle fibers in the wall of 

 the alimentary canal at this thin and constricted region, and 

 in addition to this, the wall is broken by frequent pores through 

 which the secretion of the glands of the pharynx empty their 

 products (fig. 1, GP). 



A demand to protect the delicate connection between the 

 enteron and pharynx, and the enteron itself from the sudden 

 recoil of the peculiar pharynx of Prorhynchus applanatus has 

 thus arisen. In other animals, for example, the Crustacea, 

 ''Masses of connective tissue uphold and support the various 

 and delicate tissues about them, and protect them from the im- 

 pact of surrounding organs. The largest and most regular of 

 the cells which compose this tissue are known as Ley dig's cells 

 of the first order." page 57, Dahlgren and Kepner ('08). 



As in the Crustacea, so here certain mesenchymal cells about 

 the base of this peculiar pharynx have become large and cushion- 

 like to meet the demand made for protecting the delicate enteron 

 from the impact of an adjacent organ. These form a mass of 

 conspicuous tissue which extends laterally along the posterior 

 half of the pharynx and crowds about the base of the pharynx 

 as it unites with the enterin. Anteriorily these cells form but 

 a single layer about the pharynx (figs. 1 and 2cc). 



These cushion cells in the fixed condition^ first appear as ir- 

 regular polyhedra. The largest ones measuring about 45m X 

 30/x X SO/x. The most conspicuous feature of the mature cells 

 is the greatly vacuolated condition of their cytoplasm which 

 is for the most part disposed about the periphery of the cell. 

 At some place this peripheral cytoplasm is piled up as an eccen- 

 trically placed mass of protoplasm around the nucleus. Figure 3 

 shows a section through the nucleus (A^. It also shows where 

 the large central cavity encroaches upon the peripheral cyto- 



' The specimens have been fixed in chrom-aceto-fonnalin and aceto-sublimate. 

 The former reagent have a better result. The sections were five micra thick 

 and were stained with Mallory's connective tissue stain or iron haematoxylin. 



