1 1 86 BULLETIN OF THE BUREAU OF FISHERIES. 



distinct. Head much contracted. Neck i to 1.5 mm. long by 0.21 mm. broad. 

 First proglottids 0.09 mm. broad, changing gradually until in mature proglottids 

 the length greatly exceeds the breadth. Ripe proglottids measure 0.84 to 1.4 

 mm. long by 0.18 to 0.35 mm. broad. Terminal proglottids present and fertile. 

 Sexual organs typical for Proteocephalus; uterus median, with 10 to 14 lateral 

 outpocketings on either side. Testes numerous, within vitellaria. Genital pore 

 lateral, one-third to two-fifths of length of proglottid from anterior margin of 

 same. Ovaries bilobed, median isthmus indistinct, anteroposterior diameter 

 nearly equal to breadth of both lobes. Only a few specimens obtained from a 

 single host species, Salmo scbago. 



This species approaches most nearly to P. ocellata and P. perccB among 

 known species. Unlike the new species, however, both of these older forms have 

 a fifth sucker, fewer lateral uterine outpocketings, a longer neck, differently 

 shaped ovaries, and markedly different proglottids. 



In specimens with developed proglottids the head was so much contracted 

 or distorted that any special description would be of little value. One could easily 

 observe the general features characteristic of the genus. There was no well 

 developed terminal or fifth sucker, and the end organ, which is known to replace 

 it in many forms of this genus, was inconspicuously developed, if present. 

 Personally, I incline to the view that on more careful examination this structure 

 will be found in all species, even those in which its absence has been made a 

 matter of record. Accordingly, not much weight can be put in its presence or 

 absence in any individual case.*^ 



Three plerocercoid larvae or young cestodes were found in company with 

 Proteocephalus pusillus, which I regard as young forms of this species. The 

 largest came from the salmon which was most heavily infected with this cestode 

 parasite. It was 3.15 mm. long and had begun to assume clearly the appear- 

 ance of an immature cestode. The head measured 0.3 mm. wide by 0.26 mm. 

 long, and the suckers 0.14 mm. in length by o.ii mm. in width. The neck 

 was slightly narrower than the head, but was not clearly set off from the body, 

 which was very uniform in diameter and measured 0.25 mm. in average width. 

 The posterior end of the body was swollen into a rounded knob about 0.35 mm. 

 broad and of approximately the same length. This feature was evidently 

 produced by a powerful contraction of the terminal region of the body. In 

 and near it one could see very indistinct indications of proglottid formation. 

 In form, size, and general aspect this young cestode was in full agreement with 

 the anterior regions of the mature cestodes of this species with which it was 



For a more definite discussion of this peculiar structure so variable in development in the cestodes 

 of this genus, I would refer to a paper now in press by my student, Mr. George R. La Rue, to whom 

 I am indebted for a comparison of this material from Salmo sebago with preparations of other species 

 of Proteocephalus 



