No. 2.] STRUCTURE OF TWO FISH TAPEWORMS. 36 1 



tal pore to the median dorsal line of the inner parenchymal 

 space, where a number of heavy muscle strands attach the 

 proximal end of the inner tube of the pouch firmly to the 

 dermo-muscular sac. The walls are thickest about the middle 

 of its length, and consist of a circular and transverse muscle 

 layer, with a delicate epithelium covering the outer and inner 

 surface (PI. XVI, Fig. 34). 



At the anterior end the wall of the pouch bends back, form- 

 ing a tube through the middle of the sac (PL XVI, Fig. 31). 

 This tube is lined, in the distal half, by cuticula, which is con- 

 tinuous with that covering the surface of the body. At the 

 posterior end no cuticula can be distinguished, and the muscle 

 layer is very thick. The space between the inner and outer 

 walls of the cirrus sac is filled with fibrous tissue, with many 

 nuclei (Fig. 31). The fibers run from wall to wall in transverse 

 direction toward the proximal end, while near the distal portion 

 the fibers are curved, with the concave portion directed proxi- 

 mally. At the posterior end of the inner tube the thick muscle 

 layer sends out large strands, which pass out of the proximal 

 end of the cirrus pouch and join the dermo-muscular sac, as 

 before stated. 



About the tube, within the sac, are many gland cells, pro- 

 jecting perpendicularly from its walls, and most numerous in 

 its proximal half. 



The cirrus is straight, cylindrical, and of approximately equal 

 diameter throughout, with the exception of the distal termina- 

 tion (Fig. 31, «'.). This portion is a muscular knob .02 mm. 

 in greatest diameter, composed principally of circular muscles. 

 In its normal position this terminal portion rests in the end of 

 the inner sac tube, like a ball on a cup. The sides of the dis- 

 tal fourth of the cirrus are not in direct contact with the cuti- 

 cula lining the inner tube, and throughout this distance the 

 wall of the tube is quite thick, .005 mm., and the cuticula is 

 covered with fine, stiff, bristle-like projections. The cirrus has 

 a lumen of .01 mm., which is lined by a thin epithelial layer. 

 The organ here presents a very peculiar appearance, due to the 

 circular muscles which compose its walls, and which are here 

 .004 mm. thick. Throughout most of its course the cirrus is 



