Variation in Hooks of Dog-Tapeivorms 7 



layers, and represent what are to be the prongs or sickles of the 

 mature hooks. The cone, which is open at the bottom, is devel- 

 oped to its mature size before formation of the radical portion of 

 the hook, which first appears as a horseshoe-shaped body separate 

 from the prong, but later fusing with it. The hook must be com- 

 pletely formed before the Cysticercns is eaten by the dog, or this 

 larva will not develop into the adult Taenia. As soon as the cyst 

 arrives in the stomach of the dog, it is ruptured, and the larva, 

 thus released, passes into the intestine, where it attaches itself by 

 means of its hooks to the intestinal wall. 



Kiichenmeister (1852) maintains that, after entrance into the 

 alimentary canal, the hooks grow both in size and in number ; he 

 bases his view on the fact that there is a difference in the number 

 and size of the hooks of the Cysticercns pisiforinis and those of 

 the adult Taenia serrata. He has even worked out a mathematical 

 relation or proportion between the number of hooks of the Cyst- 

 icercns and the adult stage of Cysticercns fasciolaris, showing a 

 general law governing the increase in the number of hooks in the 

 adult parasite over the original number in the Cysticercns. I may 

 state, however, that a number of Cysticerci examined during my 

 work showed a wide variation in the number of hooks in the 

 individual heads. 



From this fact it is evident that one is dealing with very irreg- 

 ular data in computing such a relation. Kiichenmeister supposed 

 that the mode of increase in the number of hooks was either a 

 development of other secondary hooks between the primary hooks, 

 or that an annual moulting of hooks occurred, two hooks being 

 added in the number developed after each moulting. In thus 

 determining the age of a parasite by means of its hooks, the 

 question arises as to the original number of hooks in each Cyst- 

 icercns, and as this number is known to be so irregular, the theory 

 is seen to be wholly unreliable. No positive evidence of moulting 

 is recorded, though Kiichenmeister cites as probable evidence 

 seven cases where tapeworms of a species not given were removed, 

 from individuals during the month of March, and bore no hooks, 

 but exhibited traces of having possessed such at some former 

 time. The suggestion followed that if the time of year for moult- 



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