STERELMINTHA. 85 



freely communicating with the nutritive canals of the adjoining 

 segments. The first joint of the Tsenia, which may be called the 

 head, differs materially in structure from all the rest ; it is in fact 

 converted into an apparatus by means of which the entire animal 

 derives its nourishment. This part in the Tsenia solium, when 

 highly magnified, is found to be somewhat of a square shape ; 

 in the centre is seen the mouth, surrounded with a circle of 

 minute spines, so disposed as to secure its retention in a posi- 

 tion favourable for imbibing the chyle in which it is immersed. 

 Around this prominent mouth are placed four suckers, which are 

 no doubt additional provisions for the firm attachment of the head 

 of the worm. In other Tsenise the structure of the oral segment is 

 variously modified : thus in Tania lata the aperture of the mouth 

 has no spines in its vicinity ; in Bothryocephalus there are only 

 two longitudinal sucking discs ; 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 mouth in a position 

 adapted to ensure an adequate supply of nutritious juices. 



(116.) The alimentary canal, which extends from the mouth, is a 

 double tube, which may be traced through the whole length of the 

 body, without any other perceptible communication with the ex- 

 terior than the oral orifice in the centre of the head : at the com- 

 mencement of every segment, moreover, there is a cross-canal, which 

 communicates with the corresponding canal of the opposite side 

 (fig. 37, 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. 



(117.) A distinct generative system is found in every segment of 

 these remarkable animals ; and, judging from the number of eggs 

 produced by each, we are at a loss to reconcile the disproportion 

 which exists between the extreme fertility of the Tsenise, and the 

 comparative rareness of their occurrence. The ovaria in which the 

 eggs are produced are of great relative size, occupying the centre 

 of each joint. In the annexed figure (fig. 37), which represents 

 one of the segments of the Tsenia solium highly magnified, the 

 ovigerous organ (&) is seen to consist of a central cavity, from the 

 circumference of which radiate a great number of csecal tubes ; 

 these at certain seasons are filled with granular ova. From 



