T. B. ROSSETER OX DREPAXIDOT.EXIA YENUSTA. 15 



After its entry into the cirrus pouch it becomes a large, swollen, 

 looped duct (Fig. 10, c"), filled with spermatozoa. The mouth of 

 the vas deferens is attached to the root of the cirrus ; it (the 

 vas deferens) occupies the whole of the interior of the pouch, and 

 thus the cirrus pouch becomes a vesicula seminalis. 



The cirrus pouch, with its cirrus, occupies the anterior portion 

 of the segment. It is an ampulla-like organ, with an elongated 

 neck; in its early stage its position is horizontal. It runs 

 laterally close under the overlapping of the segments, where they 

 unite; but as the genital papilla develops it is drawn farther 

 down, a depression is formed in the neck, and the orifice of the 

 cirrus canal is tiu^ned upwards, nearly perpendicularly. It still 

 maintains this latter position, although the pouch is sometimes 

 carried farther down in an oblique manner, caused by the 

 declension of the genital papilla. A third of the way up towards 

 the proximal end of the pouch, attached to the longitudinal 

 muscles, are the retractor muscles of the cirrus pouch ; these 

 branch off from the pouch and run some distance under the 

 ventral side of the receptaculum, attaching themselves, or coales- 

 cmg with the ring-like epithelial fold of the anterior boundary 

 of the segment. In a transverse section these longitudinal 

 muscles of the pouch are more or less exposed (Fig. 4, e) ; and they, 

 like the whole of the muscular structure of these platy helminths, 

 are non-striated. At the narrow end of the neck of the pouch, 

 the cuticle, together with the longitudinal muscles, turns inwards 

 and forms a long narrow cirrus canal ; the muscular structure in 

 its inversion attaching itself to a chitinous ring, the mouth of the 

 ciin^us canal. They (the muscles) then descend in the form of an 

 inverted cone, attaching themselves to the cirrus in the immediate 

 neighbourhood — interiorly — -of the exterior retractor, where they 

 join the epithelial longitudinal muscles. This inverted cone of 

 muscles is the elevator muscle of the cirrus. The length of the 

 cirrus pouch is 0"380 mm. ; the diameter of the pouch occupied 

 by the vas deferens is 0*070 ; and the diameter of the orifice of 

 the canal 0'034 mm. 



The cirrus (Figs. 3, and 4, c), appears to be a long, narrow, 

 flattened, pellucid rod ; such, however, is not the case : it is 

 cylindrical and opaque, with a diameter of 0*007 — O'OIO mm. 

 Previous to copulation it terminates in a small hook. Its structure 

 is composed, like the ring of the canal, of chitin. A transverse 



