161] PROTEOCEPHALIDAE—LA RUE 161 



does not cross the cirrus-pouch but lies anterior thereto until it comes 

 to the knot of the vas deferens which it passes ventrally. It forms no 

 coils anterior to the ovary but may be somewhat sinuous. The vitellaria 

 (Fig. 85) are lateral. The follicles are large, and closely packed to- 

 gether. In the posterior part of the segment the vitellaria never extend 

 posterior to the ovary as in P. per plexus. The vitelline ducts are as in 

 P. amiloplitis. The lobes of the ovary are smaller than in P. perplexus 

 or P. ambloplitis. They are more branched than in either of those spe- 

 cies but this branched condition cannot be determined except in 

 sections. 



The relations of the oocapt, ootype, oviduct, lower vagina, vitelline 

 ducts, and uterine passage are typical of the genus and need no expla- 

 nation here. The uterus is a median tube in mature proglottids. In 

 ripe proglottids (Fig. 83) the median tube has 20-25 lateral outpocket- 

 ings on either side which take up the entire ventral field of the segment 

 bounded by the anterior and posterior margins and by the ventral 

 excretory ducts. Two, three or four ventral uterine pores have been 

 observed, tho in most of the very old proglottids the ventral body wall 

 is split from end to end. The formation of the ventral uterine openings 

 is as La Rue (1909) described the process in 0. filaroides. The eggs 

 very much resemble those of P. perplexus in size but differ in having a 

 thinner and more hyaline middle membrane which is never split into 

 two layers. The embryos measure 0.014-0.0156-0.0168 mm. The second 

 membrane measures 0.026-0.031 mm. and the other hyaline membrane 

 0.027-0.033 mm. 



This species in the structure of the head stands quite by itself. 

 Its proglottids somewhat resemble those of P. perplexus but are smaller. 

 In toto preparations the ventral excretory ducts of P. singularis being 

 much larger make a fairly easy means of separation. In the number 

 of uterine pouches the two species are much alike, but these pouches in 

 P. perplexus extend farther laterad than in P. singularis. In the posi- 

 tion of the vaginal sphincter the two species are much alike but the 

 beginning region of one is dilated, in the other contracted. One has a 

 ciliated vagina, the other not. The cirrus-pouch of P. singularis is 

 more slender, the cirrus and ductus ejaculatorius are straighter and 

 more slender than in P. perplexus. 



