THE CIRRHUS-POUCH. 695 



cirrhus-pouch. As such it consists mainly of connective tissue, and 

 that of the very vesicular kind which we have already found in the 

 matrix of the worm. 



The Cirrfius-PoucJi can only be adequately studied by the method 

 of sections. From superficial preparations merely, only an imperfect 

 survey of the arrangement can be obtained. In such the cirrhus- 

 pouch simply appears as a roundish disc of considerable size (Q'4-0'44 

 mm.), which lies superiorly behind the porus genitalis, and extends 

 to the anterior margin of the joint. This disc is seen on close exami- 

 nation to be the optical section of a hollow muscle, which has when 

 quiescent a somewhat regular oval form, and is inserted on the ventral 

 surface of the joint, i.e., on the porus genitalis, usually with an anterior 

 angle of from 75 to 80. The posterior pole of the pouch usually 

 lies higher than the porus genitalis, but is, in consequence of the 

 considerable length of the pouch (O5-0 - 55 mm. in the ripe joints), 

 so nearly approximated to the dorsal wall, that it is only separated 

 by a small interval (O'Ol mm.) from the dorsal transverse muscle- 

 bands. The opposite ventral pole is different, since it penetrates 

 the transverse muscle-sheath and the whole cortical layer as far as 

 the subcuticula ; and the latter has also but a slight thickness where 

 it lies above the pouch. 



FIG. 364. Transverse section through the body of Boihriocephalus 

 latus at the level of the cirrhus-pouch. ( x 10.) 



The canal which penetrates the cirrhus-pouch is a direct continua- 

 tion of the seminal duct, and is morphologically nothing but its 

 terminal portion. Its peculiarities are secondary adaptations to 

 copulatory functions. Apart from the musculature which surrounds 

 it like a bulb, its peculiarities consist especially in this, that instead of 

 pursuing a straight course, it is rolled up in close spiral coils. This 

 is especially true of that portion of the duct which penetrates the 

 (dorsal) half of the bulb, and which, being always filled with semen, 

 serves as a sort of seminal vesicle. The portion further forward is 

 simpler ; the spiral coils are disposed in a less extensive zigzag (Fig. 

 361). Only the outermost portion opening freely at the end of the 

 cirrhus-pouch exhibits an almost straight course. It is this anterior, 

 partly stretched, partly zigzag, twisted portion of the seminal duct 

 which is evaginated by the muscular pressure of the cirrhus-pouch to 

 form the cirrhus. It differs histologically from the posterior portion 



