88 ANIMAL PARASITES. 



hooks differ even from these instruments, as in the middle 

 where the handle passes into the hooks, they have a process 

 which is certainly intended for unhooking, and which I formerly 

 called the hypomochlion. This denomination, to which I will 

 by no means adhere, is quite correct for the act of unhooking, 

 if we suppose the hook to be an imaginary double-armed lever, 

 which it resembles at the moment of adhesion, and at the same 

 time regard as the point of support, not the apex of the shaft 

 but that of the spine (hypomochlion), upon which, in unhooking, 

 the apex of the claw and the shaft as it wei'e move up and 

 down. If we omit this ideal view, the apex or root of the 

 shaft can alone be regarded as the fulcrum of the hook acting as 

 a one-armed lever, to which the force is applied, as it were, by 

 the skin of the rostellum and head and the contents of the 

 former. The spine which effects the loosening of the immersed 

 hooks supports itself in this act against the wall of the intestine 

 of the host, exactly as the packer, when he wishes to remove his 

 hooks from the bale, presses against it with the knuckles of the 

 hand grasping the handle. The knuckles of the hand, in this 

 case, exactly take the place of the spine in the hooks of Tania, 

 and in a great number of hooks the free surface of the spine 

 corresponds with the space which is formed between two knuckles 

 of the hand. We have two elevations which press against the 

 bale, or, in the hooks of the Tania against the intestine, and 

 between them a valley-like pit, into which the outer wall of the 

 bale, and with the hooks of Taenia the wall of the intestine, 

 presses ; by which means, in the latter case, the spine obtains a 

 firmer support. From this mechanism it is evident that the 

 spine furnishes at all events a temporary and subsidiary fulcrum, 

 and probably in the immersion of the hooks prevents their sink- 

 ing too deep, and consequently their breaking away during 

 removal, at the same time facilitating the latter. If we now 

 consider the circular arrangement of the hooks, it follows there- 

 from either that the adhesion takes place at once in a circular 

 surface, which is certainly admissible in the yielding walls of the 

 intestine, or that a spiral advancing movement of the head of the 

 worm is possible on and in the walls of the intestine, so that the 

 worm must at the same time twist itself partly upon its longitu- 

 dinal axis. It is difficult to ascertain with certainty whether 

 both or only one of these two kinds of movements of the hooks 

 occurs. 



