Variation in Hooks of Dog-Tapeworms 13 



The measurements given by Reinitz are those of the bladder- 

 worm (Coemirus serialis) and not of the adult parasite, and are 

 given, not for direct comparison with the hooks of the adult 

 parasite, but to show that the hooks of the bladder-worms exam- 

 ined are not less in magnitude than are some of the hooks of the 

 adult parasite examined by Baillet. This fact is to be noted in 

 connection with the discussion of the growth and development of 

 the hooks of the species under discussion earlier in this paper. 



From the above table it is seen that the range of the number of 

 hooks of the specimens collected at Lincoln corresponds to the 

 average limits given by the writers mentioned. There were ex- 

 amined at Lincoln, Neb., 28 specimens of T. serrata and 15 speci- 

 mens of T. serialis. In comparing the relative magnitudes of the 

 hooks of the two species of parasites studied, an interesting coin- 

 cidence is noted, in that the range of magnitude for character a 

 of the large hooks of T. serialis is the same as the range of char- 

 acter a of the small hooks of T. serrata. 



Comparison of the results of my measurements of hooks with 

 the measurements made by the observers mentioned shows that 

 the most striking feature of this paper is the excessive magnitude 

 of the hooks of the parasites found at Lincoln, Neb. To account 

 for this difference is a problematic matter ; yet it is not at all an 

 extreme suggestion nor improbable circumstance that geographic 

 distribution may account in part for the variation. There is also 

 a possibility of inaccurate computation of magnification of the 

 different microscopes used by different investigators. An exam- 

 ple of such an error is found in Deffke's article, where he gives 

 as magnitude of the large hooks of T. serrata, 260 fi, and of the 

 small hooks 120 //., and then gives a drawing magnified 480 times 

 according to the text. The figures of the hooks are not magnified 

 480 times, else the original hooks, large ones, were only 131 fi in 

 length, and small ones 70 p. To have the drawings given con- 

 sistent with the magnitude of the hook that is given, the drawing 

 would be magnified only about 250 times. The error may well be 

 due to a reduction in size made in connection with the repro- 

 duction of the original drawings. 



203 



