63] PROTEOCEPHALIDAE — LA RUE 63 



minimum 0.096 mm. ; sucker opening 0.058-0.080 mm. ; diameter of fifth 

 sucker about 0.060 mm. Average length of six necks 1.49 mm., maxi- 

 mum length 1.70 mm., minimum 1.02 mm.; neck narrow, up to 0.135 

 mm. The proglottids are few, numbering about 30-40. First proglot- 

 tids are broader than long, or quadrate, length soon exceeds breadth, 

 and mature proglottids are longer than broad measuring up to 0.56-0.68 

 mm. long by 0.24-0.265 mm. broad. The maximum breadth of 0.340 

 mm. was observed in a proglottid measuring 0.357 mm. long by 0.340 

 mm. broad. Segmentation is very distinct. 



The genital pore is near the middle, usually anterior thereto but 

 sometimes posterior. The vagina lies anterior to the cirrus-pouch. 

 There are about 44-66 testes and these measure about 0.159 by 0.180 

 mm. in diameter. They form two irregular layers in the region bounded 

 by the vitellaria and ovary. In many proglottids of this lot the testes 

 are not as fully developed as in the proglottids of specimens from Salmo 

 sehago. This condition facilitates the counting of the testes. The coils 

 of the vas deferens form a small mass situated for the most part anterior 

 to the cirrus-pouch. Within the cirrus-pouch the ductus ejaculatorius 

 forms a single coil and then it passes over into the small cirrus. The 

 cirrus-pouch usually extends to the middle of the proglottid or nearly 

 thereto. It has a length of about 0.111-0.150 mm. The average length 

 of eight pouches was 0.133 mm. In breadth the cirrus-pouch measures 

 0.053-0.070 mm. The lobes of the ovary are thick and are bent back 

 until they nearly meet in the median line. Vitellaria are sparse. A 

 fully developed uterus has not been observed. Of the drawings repre- 

 senting P. pusillus, figures 2, 4, and 55 were made from specimens which 

 came from Cristivomer namaycush. All the other drawings of this spe- 

 cies were made from specimens taken from Salmo sehago. 



In general these two forms agree very well but there are two points 

 of minor disagreement. These are in regard to the length of the cirrus- 

 pouch and the size of the suckers. As to the former the difference in 

 length is but a matter of a few micra and this perhaps may be explained 

 by the fact that the proglottids are in different states of contraction. 

 As for the other point of difference it may be stated that in the speci- 

 mens taken from Cristivomer namaycush the suckers are on the average 

 about the size of the suckers of the typical P. pusillus but in one or two 

 cases observed the length and breadth of the sucker is appreciably 

 larger. It is to be remembered that the measurements of the suckers 

 of the typical P. pusillus are based on a single head. Consequently the 

 range of size of suckers in that species has not been determined. Tho 

 no ripe proglottids were present in the material from Cristivomer no- 



