132 HELMINTHOZOA. 



in the Tcenia solium, when highly magnified, is found to be somewhat 

 of a square shape ; in the centre is seen a pore that has been considered 

 to be the mouth, surrounded with a circle of minute spines, so disposed 

 as to secure its retention in a position favourable for imbibing the chyle 

 wherein it is immersed. Around this apparatus are placed four 

 suckers, which are no doubt additional provisions for the firm attach- 

 ment of the head of the worm. In other Tsenise the structure of the 

 first segment is variously modified : thus, in Tcenia lata the central 

 pore has no spines in its vicinity ; in Bothriocephalus there are only 

 two longitudinal sucking disks ; in Floriceps these are replaced by four 

 proboscidiform prolongations, covered with sharp recurved spines, 

 which, being plunged into the coats of the intestine, form effectual and 

 formidable anchors ; yet the intention of all these modifications is the 

 same, namely, to retain the head in a position adapted to ensure an ade- 

 quate supply of nutritious juices. 



(343.) The alimentary canal seems to be represented by a double 

 tube, which may be traced through the whole length of the body, with- 

 out any other perceptible communication with the exterior than the 

 minute pore in the centre of the head : at the commencement of every 

 segment, however, there is a cross-branch, which communicates with 

 the corresponding tube of the opposite side (fig. 68, a), so as to facilitate 

 a free distribution of the nutrient fluids *. In some species a delicate 

 vascular network is perceptible in the parenchyma of the body, which 

 may likewise be connected with the nutritive function. 



(344.) The reproductive organs in the mature segment or Proglottis 

 of a tape-worm, each of which may be considered as an adult animal, 

 consist of a male and of a female apparatus these two sets of organs 

 being completely distinct from each other. 



The male apparatus consists of a testis, a vas deferens, and an 

 intromittent organ, the last of which is lodged in a special sac or 

 pouch. 



The testis (fig. 69, a a, b) occupies the middle of the anterior portion 

 of the body, and is of a whitish colour, owing to the spermatozoa con- 

 tained in its interior. It is composed essentially of a long csecal tube, 

 folded upon itself in close convolutions, and terminating in the vas 

 deferens (c), which reaches to the base of the intromittent organ. 



The penis (fig. 69, cZ), called also by authors cirrus and lemniscus, 

 is very variable in its form in different genera ; in its real structure, 

 however, it is merely a prolongation of the vas deferens, just as the 

 latter tube is a continuation of the testis. 



* Professor Van Beneden denies the existence of the central aperture or mouth, or 

 that the two lateral longitudinal canals with their intercommunicating trunks con- 

 stitute an alimentary system ; on the contrary, he regards these tubes as secerning 

 organs, the secretion of which is discharged from the terminal segment of the body 

 through a foramen caudale. 



