159] PROTEOCEPHALIDAE—LA RUE 159 



connect the sucker wall with the lateral or dorso-ventral surfaces of the 

 head. These probably serve a double function of causing by their con- 

 traction the deep grooves between the suckers and of pulling the adja- 

 cent margins of the suckers together, thus broadly flaring the sucker. 

 In this region the muscle-cross is weakly developed. In the lower part 

 of the head (Fig. 41) just as the suckers disappear from transverse 

 sections the fibers of the muscle-cross flare out to secure a broad attach- 

 ment on the sucker wall. In fact a great many fibers dip down below 

 and attach themselves near the lower outer margin of the sucker. At 

 the sides of each sucker large groups of very heavy muscles may be 

 found the attachments and courses of which are best made out in lon- 

 gitudinal sections. Transverse fibers, i. e. lateral and dorsoventral, pass 

 through the muscle-cross and assist in the formation of a muscle-star 

 (Fig. 41). Below this point the muscles rapidly assume the relations of 

 the muscles in the strobila. 



The longitudinal muscles of the head are fairly well worked out. 

 Certain groups which were of undetermined character in transverse 

 sections can be readily distinguished in frontal sections. The large 

 groups of tangentially cut ends (Fig. 41) at either side of the sucker 

 are in reality longitudinal muscles which come up from the neck region 

 and find their attachment on either side of the sucker (Fig. 87), right 

 and left. Much weaker muscle bands pass up toward the tip of the 

 scolex. In the apical region {Fig. 86) many heavy muscles attached 

 to the sucker wall pass out by diverging paths to the subcuticular area. 

 These probably control not only a certain part of the movement of the 

 suckers but also the form of the apex. The muscles of the head, both 

 longitudinal and transverse, are much more strongly developed than in 

 the head of P. filar oides, which the writer has worked out with great 

 care (La Rue 1910). Their arrangement in the two forms is very 

 similar, tho certain groups of muscles present in P. singularis are lack- 

 ing in P. filaroides. 



In the head the excretory vessel may be followed as coiling and 

 anastomosing trunks and vessels which are much less developed than in 

 P. ambloplitis or P. perplexus. In the neck region the anastomoses of 

 the excretory system are much like those in the head. Here four main lat- 

 eral vessels are to be found with branches which have a very few 

 openings to the exterior. A little further posteriad the excretory ves- 

 sels increase in size. This is particularly true of the ventral vessel. 

 Both ventral and dorsal vessels Jiave a very sinuous or spiral course 

 even in the most elongated proglottids. In frontal sections (Fig. 83) 

 the sinuous ventral vessels appear as series of oval or circular spaces in 

 the parenchyma. In either frontal or transverse sections the ventral 



