148 ILLINOIS BIOLOGICAL MONOGRAPHS [148 



The suckers which are deep and well muscled measure 0.30 mm. in 

 length with a sucker opening of 0.150 mm. in my specimens. Leidy's 

 measurement of the suckers was 0.375 mm. long and Benedict's was 

 0.32 mm. broad by 0.40 mm. long. In suckers of this size differences in 

 contraction states will explain the variation in size. There is no func- 

 tional fifth sucker but deep in the tissue of the head a peculiar structure 

 (Fig. 116) may be found which is a vestigial fifth sucker. Benedict 

 saw the structure but was unable to point out its significance. The neck 

 is short and 0.25-0.45 mm. wide. The first proglottids are much broader 

 than long measuring 0.344 mm. broad by 0.022-0.028 mm. long. Mature 

 and ripe proglottids are broader than long as a rule, but at times may 

 be quadrate, or even longer than broad. The last condition is rare. 

 The maximum breadth of mature and ripe proglottids is 1.5-2.0-2.5 mm. 

 while the maximum length of the same is 0.5-1.0-2.0 mm. 



The cuticula, the musculature, and the nervous system were care- 

 fully investigated by Benedict (1900) who found nothing especially re- 

 markable about these structures. The excretory system differs from 

 that of P. fossatus (Kigg.) and Corollabothrium lobosum Rigg. in hav- 

 ing no definitely placed foramina secundaria. At irregular intervals 

 along either dorsal or ventral excretory vessel arise numerous branches 

 which take a fairly direct course to the exterior. These branches are 

 of various sizes and the lumen of each undergoes considerable variation 

 in size in its course. The duct through the cuticula is very small and 

 not beset with small bristles as Kraemer (1892) described for the species 

 which he determined to be P. filicollis. No special musculature can be 

 found in the course of these ducts to the exterior. The main longi- 

 tudinal excretory vessels are four in number. They are situated just 

 within the dermo-muscular sac. The ventral vessel has the larger lumen 

 and it is further differentiated from the dorsal vessel by its very thin 

 membranous lining. The dorsal vessel has a lining apparently made up 

 of columnar epithelial cells. Rarely, however, the dorsal vessel is di- 

 lated to a size equalling that of the ventral vessel and in these cases the 

 structure of the walls of the two vessels appears to be identical. No 

 transverse vessel connecting the ventral or dorsal vessels in the poste- 

 rior part of the proglottid has been found. In the scolex there is an 

 intricate plexus of excretory vessels. Many ducts opening to the exte- 

 rior by small pores place the coils of this plexus in communication with 

 the exterior. 



The common marginal genital sinus opens about one fourth of the 

 length of the proglottid from the anterior end. It is irregularly alternate 

 in position. A genital papilla is not present. The vagina opens into the 

 sinus anterior to the cirrus-pouch. The testes are spheroidal bodies, 



