29] PROTEOCEPHALIDAE — LA RUE 29 



the latter enters the ootype. The course of these duets as described by 

 von Linstow (1891) and Kraemer (1892) was incorrect, ^^iggenbach 

 (1896) and Bendict (1900) established their true course. The vitelline 

 ducts, paired and unpaired, are made up of thin tissue possessing no 

 glandular elements. 



The vagina is a tube of varying dimensions and character leading 

 from the genital atrium to the middle of the proglottid and thence pos- 

 teriad to the interovarial space where it unites with the oviduct to form 

 the fertilization canal, which is a part of the oviduct. The vagina and 

 cirrus-pouch alike open into the genital atrium. The initial part of the 

 vagina may lie anterior or posterior to the cirrus-pouch and the opening 

 of the vagina may have either of these positions, but in some species 

 examinedj^pecially for this point the opening was dorsal to the cirrus- 

 pouch, yin Proteocephalus the vagina is usually anterior to the cirrus- 

 pouch altho there are a few species in which it is regularly posterior. 

 In species of Ophiotaenia it is as frequently posterior as anterior to the 

 cirrus-pouch, but in 0. filaroides alone it has never been observed in the 

 posterior position. In Acanthotaenia and Crepidobothrium the vagina 

 may be either anterior or posterior. The vagina on account of its vary- 

 ing structure may be subdivided into four parts. These are (1) the 

 initial part reaching from the genital atrium nearly to the middle of the 

 proglottid, (2) the tube extending back to the interovarial space where 

 its structure changes to (3) the receptaculum, and then (4) the lower 

 vagina extending from the receptaculum seminis to the oviduct. These 

 parts are distinguished by position and by structure. The initial part 

 has an opening into the genital atrium. It is lined usually by a cuticula 

 which in some species may be traced almost back to the receptaculum. 

 The initial part is frequently somewhat broadened out and is somewhat 

 muscular. Near the opening to the atrium the muscles are usually de- 

 veloped into a sphincter muscle, the sphincter vaginae. This may have 

 a strong development (Figs. 106, 183) or may be very weak (Figs. 47, 

 50, 57). The modifications of the sphincter serve as distinguishing char- 

 acters. Noticeable on the initial part of the vagina particularly but 

 also occurring on almost the entire length of the vagina are numerous 

 gland cells. 



The longitudinal tube of the vagina presents some different appear- 

 ances from the initial part. It is usually a straight or wavy thin walled 

 tube of large or small diameter depending on the species and the stage 

 of development of the proglottid. In some species as the proglottid 

 becomes mature or especially after coitus this part of the tube is much 

 dilated. In all species the musculature of this part of the tube is very 

 weak or lacking entirely. Here also the cuticula of the initial part of 



