T. B. ROSSETER ON THE ANATOMY OF DICRANOTJENIA CORONULA. 367 



abnormal, and is 0*007 mm. lower down in the genital cloaca 

 than the male genital orifice. In its early stage the orifice is, 

 like that of the male, " trumpet -shaped," with an overlapping 

 rim externally. Internally it slopes and forms a connexion with 

 the vaginal canal. During development of the vulva it becomes 

 covered by the muscular structure of which that organ is com- 

 posed, and transverse and longitudinal sections show us that the 

 interior of the orifice and vaginal canal are both smooth and free 

 from spines. The muscular coating of the orifice performs the 

 ofiice — by its contractility, which is much in excess of that of 

 the male — of a " clasping organ." 



The vulva (Figs. 5 b ?^ and 14) is an ampulla-shaped organ. 

 From its earliest stage of development it is distinct, histologically, 

 from the cirrus-pouch. In ripe segments it is a dark muscular 

 body, its composition consisting of longitudinal and circular 

 muscles. Its cuticle is covered by a dense dark mass of spines 

 -arranged like quills on a porcupine's back. Its length is 

 0-03 mm., and diameter 0*017 mm., and viewed dorsally it 

 has the appearance of being a cul-de-sac ; this is caused by the 

 abrupt course taken by the vaginal canal. 



Within the orifice the vaginal canal (Fig. 5 b o) is raised as a 

 papilla, 0-002 mm. It runs straight through the interior of the 

 vulva, makes its exit from that organ on the ventral side, and 

 runs ventrally along the dorsal cuticle of the cirrus-pouch; it 

 then curves sinuously, and makes a junction with, and forms 

 the neck and cuticle of, the receptaculum seminis. Its diameter 

 Sit the neck is 0*01 mm. 



The receptaculum seminis (Figs. 6 b p, 15, 16) is situated on 

 the ventral side of the segment, the monoscious testicular sac 

 •overlaying the posterior third of it. It is an abnormally large 

 pear-shaped convoluted sac, its cuticle being a distended con- 

 tinuation of the vaginal canal. At the neck, where the canal 

 enters the sac, I have failed to find any trace of a valvular 

 apparatus. It convolutes itself into three parts — the proximal, 

 the median, and the distal. The proximal third, through its 

 polar axis, has a diameter of O'lOl mm., and the other two a 

 uniform diameter of 0*169 mm. Its whole length is 0*805 mm. 

 The proximal third of the receptaculum lies in the dextral third, 

 and the other two in the median third of the proglottis; the 

 distal third is rounded at its base, and runs forward proximally. 



