462 W. s. NICKKRSON, 



these radial muscles the cavity of the pre-pharyux is increased iu 

 size, thus providing a means of suction and also making it possible 

 for the pharynx to be the more easily thrust forward. 



The pharynx is not in any way peculiar. It is of medium size 

 and has the ordinary form — that of a cask or barrel with a lumen 

 extending lengthwise through it. It is composed of four sets of muscle 

 fibres: radial, inner and outer circular, and longitudinal. The first 

 of these is much more prominent than either of the others. 



The inner circular fibres lie close to the cuticular lining of the 

 pharynx and are plainly evident upon the inner surface. The outer 

 circular fibres lie next to the outer surface of the body; they 

 are not numerous and are only very feebly developed, so that 

 they are to be made out only by the most careful scrutiny. The 

 longitudinal fibres lie near the exterior surface just beneath the outer 

 circle or set and are very delicate and inconspicuous. Nuclei arc 

 quite abundantly distributed through the tissue of the pharynx, but 

 I have not been able to determine their exact relations. 



The movements of the pharynx as a whole are brought ab(tut 

 through the action of two sets of muscle fibres, which are attached 

 to it on all sides near its posterior end. Some of these fibres are 

 shown in PI. 29, Fig. 5. Those of one set, the protractors of the 

 pharynx, extend obliquely forward to the body -wall and by their con- 

 traction draw the pharynx forward. Those of the other set, the re- 

 tractors of the pharynx, extend backward and are attached to the 

 wall of the intestine some distance back of the pharynx. By their 

 contraction the pharynx is drawn back. 



The intestine connects immediately with the posterior end of 

 the pharynx. It is a simple tubular sack, median iu position, extending 

 backward to very near the posterior end of the body (PI. 31, Figs. 22 

 and 23). 



Its wall is made up of two layers of muscle fibres, inner circular 

 and outer longitudinal, and a single layer of large entoderm cells. 

 The latter show great variety both in size and in form. In general 

 they seem to be larger in the more posterior portion and to become 

 gradually smaller toward the anterior end of the intestine. Some of 

 the different forms which they may assume are shown in PI. 31, 

 Figs. 25 and 2G. The nuclei are always located close to the basal 

 ends of the cells , are elliptical in outline , and show one or more, 

 often several, nucleoli perii)herally located. The free end of the cell 

 has the power of elongating in a very marked degree and the more 



