117] PR0TE0CEPHAL1DAE—LA RUE 117 



the interovarial space where they unite to form a common duct that 

 empties into the ootype. Thus far von Linstow is correct in his descrip- 

 tion of the organs of the interovarial space. According to him the va- 

 gina discharges into the ootype as do also the two lobes of the ovary. 

 He provides no visible means for the escape of the fertilized eggs from 

 the ootype. The writer agrees with Monticelli (1891:162) in thinking 

 that von Linstow has probably mistaken the oocapt for the ootype, and 

 has erroneously figured the vitelline ducts which pass near the oocapt 

 and the shell-glands lying near as discharging into it. The barrel-like 

 form of the ootype as he figures it (Fig. 167) is much more typical of 

 the oocapt. The ootype has its long axis lying lengthwise of the oviduct 

 and not perpendicular to it. The vagina in von Linstow 's figure is 

 doubtless the oviduct. There is every reason to believe that the organs 

 of the interovarial space bear the same relations to each other in this 

 species as they do in the other members of the genus. The vagina opens 

 into the common genital sinus always anterior to the cirrus-pouch. 

 "Without crossing the latter the vagina describes a curved course to the 

 interovarial space where it forms several coils. Von Linstow did not 

 mention the presence of a sphincter vaginae. The uterus has three 

 large lateral pouches on either side. A uterine pore is lacking. The 

 latter could perhaps be found after a careful examination. The unripe 

 eggs measure 0.0156-0.0196 mm. in diameter. The plerocercoid of this 

 species is found in the liver of the host in which the adult is found. 



It is evident from a study of Von Linstow 's figures and text that he 

 made several misinterpretations of the structural plan of this cestode. 

 He recognized that its plan differed in certain respects from the plan 

 on which the Taenias are formed for he said that the Taenias of fish 

 formed a distinct group in the genus Taenia. He apparently did not 

 note the marked resemblance of their plan to the plan of the Tetra- 

 phyllideans. Whether his failure to recognize the relationships of this 

 species was the cause or the effect of his misinterpretation of its struc- 

 ture cannot be determined. At any rate because of some doubtful points 

 his material should be re-examined and a comparative study made if 

 such be possible. 



This species is readily separated frOm the P. torulosus by its fifth 

 sucker, and by its somewhat smaller head and smaller suckers. The 

 ovarian lobes are more slender in this species than in P. torulosus. P. 

 longicollis is readily differentiated from P. percae by its larger head, 

 larger suckers, shorter cirrus-pouch, fewer (?) testes, fewer uterine 

 pouches and by the position of the genital pore. P. longicollis resembles 

 P. cernuae in a very few particulars such as shortness of cirrus-pouch. 

 However, P. longicollis has a larger head, larger suckers, fewer uterine 



