1 6 Earle C. Stevenson 



serrata and T. serialis hooks if they are to be used, as heretofore, 

 as a reliable basis in identifying the species. 



It is in relation to this question of determining species by means 

 of the hooks that the practical value , of this statistical work 

 exists. 



By studying a large number of hooks from several different 

 worms, an average type may be established, and many apparent 

 peculiarities and abnormalities shown to be practically common 

 factors. For instance, the shape and relative position of the 

 ventral root, barb, tooth, or radical portion of the hook, as dif- 

 ferent writers term it, is determined by observing the prevailing 

 type in a group. 



SUMMARY OF RESULTS OF OBSERVATIONS 



1. The average length of the hooks of Taenia serrata and 

 Taenia serialis found in dogs at Lincoln, Neb., is much in excess 

 of the measurements of hooks of the same parasites observed in 

 other places by different investigators. A comparison of the 

 limits in the table on page 12 will show the divergence. 



2. The correlation between characters a and b in each group 

 of hooks of both species is nearer unity than is the correlation 

 between characters a and c. 



3. The depth of the cleft in the ventral root of the small hooks 

 of both species is usually very slight. 



4. While the general form and outline of the hooks of both 

 species is quite variable in detail, yet it is practically always that 

 which is typical of the average hook. 



5. The dorsal root of all the hooks of both species is the most 

 variable in length of any part of the hook, and with the excep- 

 tion of a single head of T. serialis, character b is always greater 

 than character c. This exception occurred only in the case of 

 the small hooks of the specimen. 



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