34 T, B. ROSSETER ON THE TAPE-WORMS 



border ; on its way the vas-etferens from the other testes make 

 a junction with it, where their spermatozoa are poured into it. 

 Thence it ascends sinuously, becomes the vas-deferens, and, as 

 such, coalesces with the sperm-sac. 



The sperm-sac runs sinuously the whole width, anteriorly, of 

 the segment. In some segments its curvature is very deep, 

 adapting its sinuosity to the formation of the segment. It is 

 very attenuated, having, even when filled to repletion with 

 spermatozoa, a mean diameter of only O017 mm. Its proximal 

 end is ampulla-formed and contains the cirrus-pouch, with its 

 attendant cirrus, whilst its distal end curves downward to meet 

 the vas-deferens and terminates in a circular sphincter aperture. 

 This sphincter membrane is an outgrowth of the vas-deferens, and 

 by its contractility and the collapsibility of the sac during 

 coition it effectually closes the aperture, preventing the entrance 

 of an excess of spermatozoa. During coition the sac is completely 

 emptied of its contents, and no more sperm from the testis enters 

 to replenish it. 



The cirrus-pouch is claviform, 0'078 mm. long, and contains 

 the cirrus. The cirrus is a long, hollow, flexible rod, adapting 

 itself by its flexibility to the sinuosities of the sac. Distally it 

 resolves itself into a wavy membranous canal — vas-deferens 

 interior — terminating with a circular orifice. From the endo- 

 derm of the cirrus-pouch spring a series of protractor and 

 retractor muscles, which attach themselves to the cirrus. 



This sperm-sac, with its cirrus and pouch, cannot be considered 

 as a true vesicula seminalis, but rather as an exjDulsion-bladder, as 

 the spermatozoa are not actually stored here, neither does the 

 distal wavy cirrus membrane swell out — as in some instances the 

 vas-deferens interior does — to form a vesicula seminalis ; but, when 

 the long cirrus is everted for the purpose of coition, the spermatic 

 corpuscles pass up the vas-deferens interior, the sac is completely 

 emptied of its contents, and the receptaculum seminis, as the 

 resultant of copulation, is filled with the sperm. 



The female genital pore is distinct from, and posterior to, but lies 

 in the same plane as the male pore. The vagina is a beautiful 

 cup-shaped body, resembling in form a miniature water-lily 

 {Nymphaea alba). It is composed of a series of bent acicular 

 spines. Its concavity or vestibule is always turned towards the 

 posterior border of the segment, so that one rarely sees the orifice 



