No. 2.] STRUCTURE OF TWO FISH TAPEWORMS. 359 



presents the appearance of strands interwoven, being still more 

 open in texture than the outer parenchyma. 



Calcareous bodies are not abundant and are very small, none 

 being longer than .005 mm. 



Ne'i'vous System. — The central nervous system consists of a 

 ring a little anterior to the middle of the scolex ; a large short 

 trunk runs from the median dorsal, the median ventral, and 

 two lateral points of the ring about half the distance to the 

 cuticula, where it divides and half goes to each adjacent sucker 

 (PI, XVI, Fig. 25, n.r. and n). From the central nerve ring 

 two longitudinal trunks pass down the body just within the 

 longitudinal muscle bundles at the sides. The nervous sys- 

 tems of P. filicollis and P. avibloplitis are thus almost exactly 

 identical. 



Excretory System. — There are four regular longitudinal canals 

 traversing the body. The walls of these ducts are much thicker 

 than in P. avibloplitis , and the course of the duct is more regu- 

 lar, with fewer branches. Branches of various sizes are given 

 off at irregular intervals and take a more or less tortuous 

 course among the organs. The branches which extend toward 

 the cuticula are straighter, give off fewer branchlets, finally be- 

 coming lost in the subcuticular layer. In some cases the ducts 

 seem simply to unite with parenchyma spaces and can be 

 traced no further. In the cuticula, at rare intervals, an open- 

 ing may be found through which the excretory system connects 

 with the exterior. These openings are neither so large, so 

 numerous, nor so well defined as in P. ambloplitis. In the scolex 

 and anterior portion of the neck the four vessels are much 

 branched, the branches forming a network much as in the latter 

 species. Yet the network so formed is not so complex as in 

 P. tondosa. 



Miisculattire. — The musculature is not so strongly developed 

 as in P. ambloplitis. The longitudinal muscles are arranged in 

 numerous small bundles, appearing in transverse sections of 

 proglottids as irregular rows of dots parallel to the outline of 

 the section (PI. XVI, Fig. 23, m.l.). The sections of the bun- 

 dles are of irregular shape and vary in breadth from .0015 mm. 

 to .004 mm. 



